Till now Firefox in Windows 8-Mozilla calling as "Metro Firefox" – used a separate profile from Desktop Firefox. Things to change and news is both to share same single profile but with some exceptions, Mozilla has detailed advantages and issues with having a single profile for Firefox in desktop and Metro/modern environments.
- Since Metro Firefox won’t support add-ons, it won’t use add-ons even if they exist in the profile.
- Preferences for both modes will be kept separate.
- They’ll be offering option to switch from Desktop to Metro mode and vice versa. To be more specific, Metro Firefox will offer "Relaunch in Desktop" and Desktop one to offer "Relaunch in metro" as chrome does.
But the problem arises when you try to run both versions at the same time, if you want to do so then Mozilla suggesting you to create separate profile" using the -ProfileManager command line argument from Desktop Firefox. "
You can track the progress on shared profiles here.