How did you delete the browser? Uninstall, delete the programs folder, hard drive crash . . . . Let’s do a full clean re-install; Note: Firefox comes in three or more folders on all computers&#46; They are; Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user&#46; If you remove the Firefox folder, the user profiles would not be affected&#46; ----------- [http://www&#46;mozilla&#46;org/en-US/firefox/all/ Download Firefox For All languages And Systems] {web link} [https://www&#46;mozilla&#46;org/en-US/firefox/organizations/ Firefox ESR; Extended Support Release] {web link} Beta, Developer, Nightly versions https://www&#46;mozilla&#46;org/en-US/firefox/channel/desktop/ [https://support&#46;mozilla&#46;org/en-US/kb/install-older-version-of-firefox?cache=no Install Older Version Of Firefox] {web link} Save the file&#46; Then '''Close Firefox&#46; ''' Using your file browser, open the '''Programs Folder''' on your computer&#46; '''Windows: ''' C:\Program Files C:\Program Files (x86) '''Note:''' Check Both Folders '''Mac: ''' Open the ''' "Applications" ''' folder&#46; https://support&#46;mozilla&#46;org/en-US/kb/how-download-and-install-firefox-mac '''Linux: ''' Check your user manual&#46; If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it&#46; See Install Firefox on Linux; https://support&#46;mozilla&#46;org/en-US/kb/install-firefox-linux If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory&#46; http://www&#46;mozilla&#46;org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any '''Mozilla''' or '''Firefox''' program folders&#46; Do not remove the '''Mozilla Thunderbird''' folder if there is one&#46; '''Do Not''' remove any profile folders&#46; After rebooting the computer, run a registry scanner if you have one&#46; Then run the installer&#46; +++++++++++++++++++++++++++ If there is a problem, start your '''Computer''' in safe mode and try again&#46; [http://encyclopedia2&#46;thefreedictionary&#46;com/Linux+Safe+Mode How to Start all Computers in Safe Mode;] {web link} Free Online Encyclopedia

Do you mean you had Firefox Nightly 94.0a1 installed and that you somehow lost its profile or other profiles ? You can't safely downgrade a profile to a previous version, especially a Nightly profile and profiles are also locked against a specific installation folder. *https://support.mozilla.org/en-US/kb/dedicated-profiles-firefox-installation *https://support.mozilla.org/en-US/kb/understanding-depth-profile-installation *https://support.mozilla.org/en-US/kb/recover-user-data-missing-after-firefox-update If you did uninstall Firefox and choose to remove the profile then all profile in the Firefox version have been removed and you would have to use an undelete utility to recover a lost profile. Note that the Nightly builds are meant for experienced testers and can be unstable at times and updates twice per day.