A Graphical User Interface (GUI) for allowing you to select a specific Profile from among the different user Profiles you may have in your installation(s) of Firefox. The average user with only one Profile, will not normally need or even see the Profile Manager dialog box. But if you do need it, it can be an invaluable tool for solving problems with the Firefox browser.
This is what my Profile Manager dialog box looks like with my various installations of Firefox.
Profile Manager dialog box functions/controls
Create a new Profile
Rename an existing Profile
Delete a Profile
Start Firefox from the dialog box
Exit the dialog box
tick - to work offline
tick - to have the Profile Manager dialog box appear whenever you startup Firefox