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.

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.