Container Tab is a new experimental feature that is available in Firefox 50 Nightly currently that can be best described as profiles lite. We talked about the feature back when it was called Contextual Identities.
Firefox supports profiles which you can use to run different copies of the browser that are completely independent from each other.
Each profile has its own profile folder with storage, temporary files, extensions, cookies, preferences, and anything else that is either user created or automatically added.
Container Tab uses a similar concept. As Mozilla puts it, they allow users to "separate different contexts while browsing the web on Firefox".
One core difference to profiles is that containers are opened under the same profile. So, instead of having to configure Firefox to launch different profiles for various activities using shortcuts, a Firefox user would simply launch one of the available containers instead for that.
It is rather interesting that Mozilla choose to use containers this way considering that one reason for blocking the integration of private tabs in Firefox was that having different contexts in the same browser window would confuse users.
Note: Container Tab is an experimental feature that may or may not land in Firefox Stable. Additionally, it may change before it is released.
Containers are enabled by default on Firefox 50 Nightly. You can open a new container with a tap on the Alt-key, and the selection of File > New Container Tab from the context menu.
There is also a new icon that you may drag and drop on one of Firefox's toolbars to access the functionality using it instead.
The four containers personal, work, banking and shopping are available currently. Each acts separately from the others and the default container.
Containers are easily distinguishable by their color in the Firefox tab bar. Mozilla displays the container type on the rightmost side of the address bar on top of that.
Container names are suggestions, but they don't limit what you can do when using them. You can use the banking container to check a second Gmail account, or Shopping for watching YouTube videos without being signed in.
You are probably wondering who containers differ from profiles. I already mentioned that containers all work under a single profile.
Containers use individual browser storage that is completely separated from the default container and any other container that is open at the same time.
Browser storage refers to data such as cookies or localStorage that is saved to the local system by the browser.
The following data is separated by containers:
Sites that you open in a container have access to that container's browser storage, but no access to any other browser storage.
Containers share data, which is different from profiles where this does not happen. All containers get access to saved passwords, the browsing history, bookmarks, saved form data or security exception.
Containers improve privacy for users when used correctly. You could separate social media sites from your regular browsing session for instance, or avoid ad retargeting by opening shopping sites in their own container.
Another handy effect of using containers is that you can open different accounts on the same site at the same time. Open three Gmail accounts in the same Firefox window, or a work and personal Google account.
Mozilla plans to add custom container options to the feature in the future, and considers site-specific containers as well.
Especially the latter seems useful as they could help users in several ways:
The following questions remain unanswered for now:
Container Tabs can be a useful feature, especially for users who sign in to different accounts on the same site using different Firefox profiles or browser extensions.
The introduction of site-specific containers should improve privacy and security significantly as well.
One question that cannot be answered right now is how regular Firefox users would perceive the feature. It seems complicated to use but I guess that Mozilla could provide automation to some of that in the long run.
I'd probably use it only for signing in to different accounts on the same site at once. But what about you?
You can follow the progress Mozilla makes on Bugzilla.
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