• Every profile has its own set of bookmarks, extensions, themes and browsing history.
• If one instance of Firefox crashes, it will not bring down other instances of Firefox running under different profiles.
• The only thing shared between profiles are the plugins (Java, Flash, etc).
• Separate profiles can be used to run different versions of Firefox at the same time.

Here’s how it’s done:

1. Launch the profile manager to create a new profile:
   “C:\Program Files\Mozilla Firefox\firefox.exe” -profilemanager

   

   Make sure you close all current instances of Firefox otherwise it will simply open a new window instead of the manager.

2. Create a new profile. I would recommend using a single lowercase word.
3. Modify your Firefox shortcut to look like this:
   “C:\Program Files\Mozilla Firefox\firefox.exe” -P “profile-name”

   

4. Now that you’ve setup separate profiles, you still need to tell Firefox to run them independently of one another, by adding the “-no-remote” option to one or both of your shortcuts:
   “C:\Program Files\Mozilla Firefox\firefox.exe” -P “profile-name” -no-remote

-no-remote allows you to run multiple profiles simultaneously, otherwise any new request to open a Firefox window will simply attach the window to the profile that’s already running.
-no-remote effectively tells Firefox to open an independent instance of the indicated profile.

The disadvantage of the -no-remote option is that it limits you to one instance of a profile at any given time, so clicking twice on a Firefox shortcut that has the -no-remote parameter will give you the following error.

Getting around this is fairly simple: only add -no-remote to the profile that you expect to use less often.