If you share your desktop, occassionally require a big set of Firefox extensions or use your browser for various, accurate applications, you should consider using multiple profiles.
You can keep one Firefox installation with different, independent preferences, looks and sets of extensions.
When you launch Firefox, it can ask which profile to run.
Is it really useful? It depends on how you use your browser. It may be a good way to secure your passwords and not waste system resources on dispensable tasks performed by extensions which you do not currently need.
Set multiple Firefox profiles
Start with closing Firefox (all windows, including downloads).
You need to open the Profile Manager.
In Windows you need to press Windows key + r to open the run line.
A new window will appear. Type firefox.exe -ProfileManager
In Linux, go to the Firefox directory and start Firefox with ./firefox -ProfileManager command.
Once you get the Profile Manager window, you need to be careful. Otherwise, you may easily remove your existing profiles including all the settings.
Managing profiles is pretty straightforward from now on. Let’s add a new profile.
Press “Create profile” button.
You will run Create Profile Wizard. Click Next.
Choose a rational name for your profile (e.g Work or John) and optionally change the profile directory pressing “Choose Folder…” button. Click Finish.
That’s it! You have successfully created a new profile. You will probably want to untick the “Don’t ask at startup” box in the Profile Manager. Otherwise, Firefox would open the same chosen profile every time it would be run. If you untick the box, it will run the Profile Manager at startup.
Shortcut to the chosen profile
If you use your default profile most of the time, choosing it at each startup of Firefox may get a bit irritating. However, you can bypass it by creating a shortcut to the chosen profile or running Firefox from the command line with appropriate flags.
You can select the profile you want to run with -P flag. Let’s try it. Close Firefox, open the command line (Windows key + r for Windows) and type firefox.exe -P "name of profile" (case sensitive, include quote marks!). Firefox will open the chosen profile without opening the Profile Manager window.
Now we can create a shortcut to the specific profile. Right click on the Desktop or in the desired folder and choose New » Shortcut.
In new window type the path of firefox.exe file with the profile flag, normally "%ProgramFiles%\Mozilla Firefox\firefox.exe" -P "name of profile" will work for Windows.
Click Next, type the desired name of the shortcut and click Finish. You get a new icon, which opens Firefox with the profile you selected.