When you uninstalled Firefox, hopefully you didn't choose to remove your personal data, since that would of course wipe out your old profile.

If you check the following places, can you find any profile folders that Firefox is not seeing?

• Windows desktop: Old Firefox Data (profile folders are moved here during the Reset process)

• Default profile location: type or paste the following in the Start menu search box and press Enter (or use a Windows Explorer window):

%APPDATA%\Mozilla\Firefox\Profiles

See:

• https://support.mozilla.org/kb/how-run-firefox-when-your-profile-missing-or-inacc

This is usually caused by a problem with the profiles.ini file and the profile marked as Default=1 in this file is no longer present on the hard drive.

• Windows: %AppData%\Mozilla\Firefox\
  C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\
• Linux: ~/.mozilla/firefox/
• Mac: ~/Library/Application Support/Firefox/

You can use one of these to make Firefox create/use a new default profile:

• Delete the profiles.ini file to force Firefox to create a new default profile
• Use the Profile Manager to create a new profile
• Use "Choose Folder" when you create a new profile to select the location of a lost profile and recover this profile

• http://kb.mozillazine.org/Profile_Manager
• https://support.mozilla.org/kb/Managing+profiles
• http://kb.mozillazine.org/Profile_folder_-_Firefox