Separate Instances of Firefox
With a Firefox window already open, if you open another Firefox window (not a new tab), the second window – and all subsequent Firefox windows – will use the same firefox.exe process. Cookies and sessions will be shared across all these Firefox windows. So if you are logged in to Gmail in one window, and open Gmail in another window, it will log you in straight away. This makes it difficult to be logged in to more than one Gmail account using Firefox.
Another implication is that if Firefox crashes, all Firefox windows will be affected.
I prefer each Firefox window to run in its own process and not to share sessions. The solution that I found involves the creation of separate profiles for each. A Firefox profile includes bookmarks, history, and add-ons. There may be a way to copy profiles but I haven’t tried it out myself.
The first step is to amend your Firefox shortcut by appending -no-remote -ProfileManager. Each time you launch Firefox, you will see the Profile Manager window:
Here you can create a new profile or launch an existing profile. To copy an existing profile, you could try to manually copy the contents of the profile directory which by default is in C:\Documents and Settings\username\Application Data\Mozilla\Firefox\Profiles. But do be careful as there are some hardcoded values, e.g., the pathnames in extensions.ini.
Note: UI developers could also use this method to run Firefox 2 and Firefox 3 side-by-side for testing purposes.
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