Unable to open firefox 10 profile manager

The profile manager will only open if there are no other Firefox windows open, so make sure Firefox is properly closed. You can add -no-remote to the shortcut to get around that.

Having said that, the built-in profile manager is probably going to be depreciated. Instead, a separate application will handle it. A pre-release version is available.

https://wiki.mozilla.org/Auto-tools/Projects/ProfileManager

As optional has described, if an instance of Firefox is already open, you have to add -no-remote: firefox.exe -p -no-remote

Firefox Commands

You can use -no-remote at anytime to open the profile manager.
You only can't open the profile manager if the -no-remote switch isn't specified and Firefox is running.

See also:

• http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox
• http://kb.mozillazine.org/Opening_a_new_instance_of_Firefox_with_another_profile