Firefox saves your personal information such as bookmarks, passwords, and user preferences in a set of files called your profile, which is stored in a separate location from the Firefox program files. You can create multiple profiles, each containing a separate set of user information. Through the Firefox Profile Manager, you can create, remove, and rename profiles, but only one profile will be active at a time.
How to create a profile?
Profile manager is not available through regular menu, so you need to run the command to get profile manager.
There are 2 ways to get the profile manager;
1. Open the Run dialog in using Windows+R key. Type in firefox.exe -ProfileManager. This will open up Firefox Profile Manager
2. Open Command prompt and type “C:\Program Files\Mozilla Firefox\Firefox.exe” –ProfileManager
When you open Profile Manager for first time, there will be only one default profile and you can create multiple profiles here. Uncheck the “Don’t ask at Startup” check box so that each time when you open Firefox it asks which profile to load.
You can also create shortcuts for each profile, so that you can directly go to the profile. To do this, first create a shortcut on your desktop, Right click and select properties. In the target box, enter -P PROFILENAME. Replace PROFILENAME with the name of the profile you want to run.
Now you can run any profile directly from your desktop. With different profiles, you can create different Firefox environments, you can test add-ons and themes in one profile without effecting the other profiles.