You can have multiple Firefox profiles, each containing a separate set of user information. The Profile Manager allows you to create, remove, rename, and switch profiles. If you have (or plan to have) multiple installations of Firefox on one computer, see Dedicated profiles per Firefox installation. The Refresh Firefox feature can fix many issues by restoring Firefox to its default state while saving your essential information. If Firefox is open, close Firefox: and select Exit. Click the Firefox menu at the top of the screen and select Quit Firefox.”]
Source: https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles