The Firefox web browser supported profiles for a very long time. Profiles are separate browsing profiles that run independent of each other. User generated content, bookmarks, installed add-ons, or the browsing history is kept separate from other profiles, and so are settings, custom about:config modifications, or any other change made to the browser.

Firefox users and admins used the Profile Manager to create new user profiles and manage existing ones in the past (and still do as it still works fine).

You can check out Firefox command line options overview for details on running the Profile Manager; essentially, you have to add -p when you start Firefox to have it launch the profile manager, and need to add -no-remote to the command if you want to run multiple profiles at the same time.

You can run multiple Firefox profiles for work and for specific tasks as profiles offer a better way of separating data and customizing the browser to different requirements.

Mozilla planned to replace the original Profile Manager with a new tool back in 2011 but nothing came out of that even though it is still possible to download the new tool the organization created back then and run it.

The organization did introduce the about: profiles internal page in Firefox in 2015 to move profile management into the browser.

about: profiles in Firefox

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The about: profiles page is available in all supported versions of the Firefox browser. You can load the address in Firefox Stable or Firefox Nightly.

The description at the top explains what About Profiles is all about:

This page helps you to manage your profiles. Each profile is a separate world which contains separate history, bookmarks, settings and add-ons.

Three core options are displayed at the top:

1. Create a new user profile.
2. Restart the Firefox browser with add-ons disabled.
3. Restart Firefox normally.

Restart options are self-explanatory; Firefox launches a profile creation wizard when you select the create new user profile option on the page.

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The wizard walks you through the steps of creating a new profile in Firefox. You may select a custom name for the profile and even change the default folder if you want to.

The profile is ready for use right after you hit the finish button to create it.

Manage profiles

You find the list of existing profiles below the three general options. Each profile is listed with its root directory and local directory, and whether it is the default profile of the browser. The default profile gets loaded automatically when you don't supply other instructions on start.

Up to five options may be displayed that you can activate for profiles:

1. Rename -- always available. Renames the profile name.
2. Open Folder -- always available. Opens the folder of the profile in the default file browser of the operating system.
3. Remove -- only available for non-default and not in use profiles. Deletes the entire profile. There is no backup but Firefox displays a prompt that requires confirmation and explains that the data cannot be restored once the user gives the okay.
4. Set as default profile -- only available to profiles that are not the default. Changes the default Firefox profile to the selected one.
5. Launch profile in new browser (Firefox 63) -- Opens a Firefox instance using the selected profile.

Some of the options are really useful. Rename may come in handy if you did not pick a custom name for a profile, and remove helps you clean up profiles. The option to launch a profile in a new browser is new and useful if you need to run a profile in a new browser instance next to the existing one. Note that the profile will open in the same Firefox version which may not always be what you want.

Tip: You can create desktop shortcuts to load profiles and different versions of Firefox with just a click.