You could use it to hide that you are shopping for Christmas presents, looking for medical issues or to avoid embarrassment when your better half discovers that you are interested in watching Spring Break parties on your computer.

The private browsing mode can be started from the Tools > Start Private Browsing menu, or with the keyboard shortcut Ctrl-Shift-P. Firefox will save all tabs in a session, exit, and open anew in the private browsing mode. You can also autostart Firefox in private browsing mode if you want your browsing sessions to be cleared automatically all the time.

Open in Private Browsing Mode is an extension for the Firefox web browser that adds functionality to open links in private browsing mode to the web browser. The add-on does not change the fact that the current browsing session will be saved before the private browsing window is opened. It merely makes the whole process more comfortable.

When you encounter a link that you want to open in private browsing mode, you’d otherwise have to copy it manually, start the private browsing mode, and paste it into the address bar to load it in that mode.

With the add-on installed, you simply right-click the link and select the Open Link in Private Browsing Mode option from the context menu to do so.

You can also start a private browsing session without opening a link. Just right-click anywhere on the page and select the open private browsing mode option to do so. Even better; you can switch back to normal mode with a right-click on a page in private browsing mode.

Open in Private Browsing Mode is a useful extension for Firefox users who make use of the browser’s private browsing mode. The extension can be installed from the official Mozilla add-on repository. Chrome users can use Ghost Incognito for similar functionality.

The situation is different on public PCs, work PCs and other shared computer systems as it is usually a good idea to protect your privacy from the prying eyes of others. Sometimes it may even be essential to avoid the leaking of work secrets or other confidential data.

Chrome’s Incognito Mode works much like the other private browsing modes. Users can start it with the shortcut Ctrl-Shift-n or a click on the Wrench icon and the selection of New Incognito Window from the context menu.

Incognito Mode blocks the writing of permanent session data. This includes the browsing and search history, cookies or cached files. When users select to run the mode, a new window is launched. Incognito Mode is indicated by an icon in the upper left corner and information on new tab pages.

One of the issues with Chrome’s Incognito Mode is that it is not possible to configure default actions for domains. Whenever you want to launch a site in the private browsing mode, you need to perform the same steps. An automated solution would make the experience more comfortable and secure, as it would eliminate the possibility of forgetting to launch a site in the mode.

Ghost Incognito is a free extension for the Google Chrome web browser that maintains a list of domain names that should always be loaded in Chrome’s Incognito Mode.

The extension adds an icon to Chrome’s address bar. A click on the icon forces the browser to load the active domain in Incognito Mode whenever it is loaded. The current website will be loaded in Incognito Mode right away, and the same happens if the website is opened in future browsing sessions.

The list of domains can be cleared completely. Users who want to clear specific domains only first need to allow the extension to run in Incognito Windows. The extension icon then appears in those windows where it can be clicked to remove the domain from the listing.

There is no way of telling which domains have been forced to run in the private browsing mode.

Chrome users can download and install the Ghost Incognito extension from the official Chrome web store.

Incognito Mode spawns a new window every time it is activated. Activation is done by either pressing Ctrl-Shift-N or clicking on the wrench icon and selecting New Incognito Window from the context menu.

Users who want to always open a website or domain in Incognito Mode have to do so manually on every browsing session as there is no option available to automate that process.

That’s where the Chrome extension Autonito offers to step in. The extension offers to store a list of websites and domains that should always be launched in Incognito Mode in the browser. Autonito spawns an Incognito window automatically whenever one of the stored domain names or IPs is loaded from bookmarks or manually in the address bar.

It basically automates the process so that selected websites and domains are always opened in Incognito Mode in the browser. The list of sites and IPs is managed in the extension’s options.

Sites are added from a simple form on the options page. Chrome users need to enter the domain or IP exactly, www.example.com and example.com are for instance two different domains. Sites can be removed with a click on the delete button next to each site listing.

Autonito is available for direct installation at the Chrome extensions repository.

Update: The Autonito extension for Google Chrome has been removed from the Chrome Web Store. Alternatives are thankfully available. Among them Incognito Regex which uses regular expression matches to launch websites or domains in Chrome’s Incognito Mode or Ghost Incognito to add domains to a list of sites that are opened in the private browsing mode automatically.

Users naturally feel safer using that mode, but that should not be the case. Why? Because there are means to find out which sites have been accessed in private browsing mode.

You see, one feature of the Windows operating system is a DNS cache, that stores domain name and IP links. Without going into to much details, the DNS cache records information about every website that the user opens in a web browser in Windows.

Curious Windows users just need to list the contents of the DNS cache to find out what websites a user has been visiting in private browsing mode. It may require some additional comparisons to find the private browsing mode websites, but that requires just some manual work and can be neglected.

Here is how you can display the contents of the DNS cache:

• Open a command prompt in Windows. The easiest way to do that is to press Windows-R, type cmd and the enter key.
• Now type the command ipconfig /displaydns in the command prompt and hit enter.
• This displays all websites that have been stored in the DNS cache. Please note that this includes everything, which means websites in all web browsers, regardless of whether they have been opened automatically (e.g. by a script on the site) or manually by the user.

Chance is the list is to large for the command line cache. You can use the command ipconfig /displaydns > dns.txt to save the output in the text document dns.txt. It is then possible to open the document in a text editor, to see all records. Opening it in a text editor has other advantages, like being able to search through the records.

Windows offers an option to flush the DNS cache so that all records are deleted from the cache. This is done with the command ipconfig /flushdns.

Some programs (like CCleaner) offer options to delete the DNS Cache. It is also possible to write a simple batch file to delete it on shutdown. Let me know if you like an example script that does that.

Windows users who regularly work in private browsing mode should consider clearing their system’s DNS cache frequently to protect their privacy.

First problem, the report is not online yet. Cnet linked to an old report that contained limited information on the subject, as it was published in August 2009. Only an abstract of the new report is available on the USENIX website.

We study the security and privacy of private browsing modes recently added to all major browsers. We first propose a clean definition of the goals of private browsing and survey its implementation in different browsers. We conduct a measurement study to determine how often it is used and on what categories of sites. Our results suggest that private browsing is used differently from how it is marketed. We then describe an automated technique for testing the security of private browsing modes and report on a few weaknesses found in the Firefox browser. Finally, we show that many popular browser extensions and plugins undermine the security of private browsing. We propose and experiment with a workable policy that lets users safely run extensions in private browsing mode.

So, what are the findings of the report according to Seth? The private browsing modes of Firefox, Google Chrome, Internet Explorer and Safari are not necessarily as private as the developer’s claim.

Why is that? Because add-ons may undermine the mode. While the browsers do not store data in private browsing mode, add-ons or extensions may very well do so. There are simply no control mechanisms yet to prevent them from doing so.

But that’s something that the Mozilla Firefox developers have already recognized in February, 2010.

But even if add-ons record activity it may not mean that the privacy is compromised. That largely depends on the data that is stored and how it is stored and made accessible in the browser. Another consideration is that Google Chrome for instance, disables all extensions by default, but gives the user the controls to enable them in private browsing mode.

Lastly, the study did not include the Opera web browser which it should have. What does this all mean for users who use the private browsing mode? That depends. First on the add-ons that they use, and if some store records of private browsing sessions, and second on the dedication and technical knowledge of users who want to spy on someone else’s web browsing sessions.

Browser developers like Mozilla should consider adding a no-extensions policy to the private browsing mode of Firefox, to prevent data leaks in the mode. A more sophisticated solution, like only enabling extensions that are known not to record data in private browsing mode, should be the ultimate goal though.

Google Chrome users can launch the private browsing mode manually in the web browser, or automatically by launching the web browser with the private browsing startup parameter.

The Chrome extension Autonito adds a third possibility. Chrome users can define websites in the extension that should always be loaded in incognito mode. Websites are added or removed in the extension’s options. The extension will automatically launch a new incognito window whenever a Chrome user clicks on a link pointing to a website included in the list, opens the site from the bookmarks or enters the site url into the address bar.

The extension currently has difficulties with cookies, which are stored in the browser. It is likely that the developer will update the extension as this is a known issue. It is however possible to work around that issue.

google chrome incognito

It is possible to block cookies from specific websites in the Chrome options. Open the Chrome options by clicking on the Tools icon and selecting Options from the context menu. Switch to Under the bonnet, and click on the Content Settings button.

A click on Exceptions displays the configuration menu to add cookies to a whitelist or blacklist. Simply click on Add, enter the domain name in the pattern field, and select Block from the available actions.

block cookies

Autonito can automate the usage of the incognito mode in Chrome. The only possible problem that we see is that the list of sites that are automatically launched in incognito mode is available in the browser. But the list does not necessarily mean that the site is visited by the user who has configured it.

Autonito can be downloaded from the official Google Chrome Extensions Gallery.

The incognito mode can be started by pressing Ctrl-Shift-N or by selecting New Incognito Window from the tools menu in the browser toolbar.

There is however no option to open an existing website in incognito mode.

Incognito Switcher is an extension for the Google Chrome browser that can do just that. The extension adds an icon in the Chrome address bar that provides access to this functionality.

A click on the button will change the state of the current tab from normal mode into incognito mode and vice verse.

A double-click on the icon will switch the whole window to incognito mode and back to normal mode.

It should be noted that switching a tab or window to incognito mode will not remove the records that already exist in the browser, only future records will be removed by the private browsing mode.

This makes it for instance interesting when an Internet user encounters wants to open links on a current website in incognito mode.

Keyboard shortcuts can be configured in the options of the Chrome extension to switch to or from incognito mode with the keyboard.

Incognito Switcher can be downloaded from the Google Chrome extensions gallery.

The latest versions of Chromium, the Open Source core of Google Chrome, outline another interesting feature that will be available soon in the web browser as well: Allowing extensions to run in incognito mode.

Incognito Mode is the private browsing mode in Google Chrome. This mode prevents that data from that browsing session will be recorded in the web browser so that no traces of it can be found after ending the session.

No extensions are enabled by default and in previous versions of the web browser. The main reason for this behavior is that some extensions do record data which could interfere with the incognito mode.

The latest Chromium releases now give the user the choice whether to enable an extension in incognito mode. It would for instance be no problem to activate extensions that do not record data so that they can be used in incognito mode as well.

The option to allow extensions to run in incognito mode is available in the Google Chrome extension manager. Placing a checkmark in the “Allow this extension to run in incognito” box will enable that extension in the private browsing mode.

The feature is currently only available in Chromium with the likelihood that it will be implemented in one of the next Google Chrome development version updates.

This behavior is changed by the Firefox add-on Private Browsing Window which – as the name suggests – provides the means to launch a private browsing session in a new window without closing the standard session first.

The extension adds a Private Browsing Window link to the Firefox Tools menu and to the status bar of the browser. A click on the link or button will launch a new Firefox window in private browsing mode. The extension will display an add-on installation dialog upon first usage that tries to install the Private Browsing Window Helper extension. This extension is not required for the core functionality. It does however improve interaction between non-private and private windows. It specifically adds an option to open links in the non-private or private browsing windows.

Private Browsing Window makes it a tad easier to work with the private browsing mode in Firefox. The extension is available for Firefox 3.6 only and can be downloaded from the official Mozilla Firefox add-on gallery website.

Update: The Firefox add-on has been discontinued as it is not necessary anymore. The Private Browsing Mode can be launched via the Tools > Start Private Browsing menu or with the keyboard shortcut Ctrl-Shift-p.

One exception to that rule is Flash content, so called flash cookies or local shared objects, are still stored on the system and an analyst could use those to uncover the websites that stored them on the computer even in private browsing mode.

This is going to change with the release of Flash 10.1 which will automatically recognize the private browsing mode and abide to its rules. This essentially means that Flash Player 10.1 will automatically clear any data that has been created during the private browsing session so that this data cannot give clues about the websites the user visited during that time.

Private Browsing mode is currently supported in Internet Explorer 8, Mozilla Firefox 3.5 and Google Chrome 1 or higher. Safari 2 is also offering private browsing mode which is currently not supported by Flash 10.1 (but will be in the future).

Flash content that has been stored on the computer system before starting the private browsing mode will remain on the computer. They will however be inaccessible during private browsing mode.

Starting with Flash Player 10.1, Flash Player actively supports the browser’s private browsing mode, managing data in local storage so that it is consistent with private browsing. So when a private browsing session ends, Flash Player will automatically clear any corresponding data in local storage.

Additionally, Flash Player separates the local storage used in normal browsing from the local storage used during private browsing. So when you enter private browsing mode, sites that you previously visited will not be able to see information they saved on your computer during normal browsing. For example, if you saved your login and password in a web application powered by Flash during normal browsing, the site won’t remember that information when you visit the site under private browsing, keeping your identity private.

Flash Player will not store any changes made to the Global Settings Manager which does have a consequence if a web site or application requests additional storage space. The request will simply be denied which is why the Adobe developers have increased the default local storage limit in private browsing to 1 MB (opposed to the 100 KB default in normal mode).

Flash Player does not save any information—including settings—in private browsing mode, since this information might reveal sites that you visited while using private browsing. Accordingly, settings options will be hidden. Tabs that modify domain-specific settings such as privacy (camera and microphone access) and local storage will not be displayed. Since you cannot set domain-specific settings in private browsing mode, Flash Player will use default settings from the global Settings Manager.

Additional information about Flash Player 10.1′s new private browsing support are accessible at the Adobe Devnet.

Most web browsers come with a switch to enable private browsing mode once the web browser has been started. The option in the Firefox web browser is available under Tools > Start Private Browsing or by pressing the Ctrl Shift P keyboard shortcut.

This can be a nuisance for some Firefox users who prefer to always browse the Internet in private browsing mode. This can for instance be interesting for users who use a portable version of Firefox on an USB stick to prevent that data gets stored on the system they use Firefox on.

Firefox comes with a configuration switch since version 3.1 which can be set to true to turn on private browsing mode automatically whenever the web browser is started. The following steps need to be performed to autostart Firefox in private browsing mode:

• Enter about:config in the Firefox address bar. If that is the first time click on the I’ll be careful button.
• Paste browser.privatebrowsing.autostart in the form at the top to filter for the entry needed.
• Double-click the entry. This will automatically change the value from false to true.

Firefox will start up in private browsing mode on the next start of the browser. The changes can be undone by performing the same steps that are outlined above.

This may however be not the only problem associated with private browsing. A recent paper by security researcher Kate McKinley confirms deficiencies in all web browsers and especially in Apple’s Safari. Not only normal cookie and data handling was tested but also plugin related handling of Flash and Google Gears data. The surprising result was that no browser passed all private browsing tests.

In fact, all of the existing private browsing modes have some form of data which is not cleared when users enter or leave private browsing modes. Although Chrome cleared the only tested type of data it stored, it was surprising to find that Gears data was not cleared, since Gears is included in the browser. However, this behavior is consistent across all browsers tested, as we will see later.

Firefox 3.1 Beta 2 clears cookies and session storage properly, but the persistent storage (window.globalStorage) is preserved between a normal and private browsing session.With IE 8 (Beta 2), both cookies and session storage were cleared properly, however the IE user Data stores were not cleared between the normal and private browsing sessions.

Safari on Windows fared the worst of all in these tests with respect to private browsing, and did not clear any data at all, either before entering or after exiting the private mode. On OSX, Safari’s behavior was quirky; in no case was the HTML 5 database storage cleared before or after private browsing. Previously set cookies seem to continue to be available if the user entered a private browsing session, but if the user started the browser and went directly into private browsing, it seemed to behave as expected.

All browsers have troubles with Flash Cookies and their private browsing modes. This is largely due to the way Flash Cookies are created and stored (without user interaction and means to display warnings). So what’s the conclusion in this matter? Users who like to use the private browsing mode should not use Apple’s Safari in its current stage. They should also make sure to either disable Flash and other third party plugins or use settings that prevent them from acting automatically (for example by using NoScript in Firefox).

Check out the Flash Cookies Explained article if you want to read up on Flash Cookies and find out where they are stored and how they can be deleted from a computer system.

It is important to note that private browsing is only helpful to avoid records of browsing sessions on the computer used. It does not hide the user from the Internet Provider or websites that they visit.

Private Browsing can be enabled in the Firefox Tool menu. It will display a popup that contains information that private browsing mode will be started and all currently open tabs will be saved to be reopened after the private browsing session ends.

Firefox will not record browsing history, search history, download history, web form history, cookies and temporary Internet files. Bookmarks as well as downloads on the other hand will be retained in private browsing mode.

Firefox will add the (private browsing) string to the title which is a indicator for anyone that Private Browsing is enabled. Private Browsing can be disabled from the Tools menu again by selecting the same menu entry that activated it.

Users who regularly clear data when closing Firefox might wonder why they should be using the Private Browsing mode at all. The main difference between clearing data when closing the browser and using the Private Browsing mode is that the Private Browsing mode will never store data on the hard drive. This might however happen when cleaning Firefox data by closing the browser. First, data could be recovered and second it will still be there if Firefox closes unexpectedly.