Mozilla’s macOS Firefox browser saves cached files on the Startup Disk. This can lead to a shortage of space. Here’s how you can reset Firefox to recover some of that storage.
When you use the Mozilla Foundation’s Firefox web browser on your Mac, it generates a profile folder and configuration files in ~/Library/Application Support/Firefox. The folder consists of the Profiles folder and the profiles.ini file. The Profiles folder contains subfolders which store individual profiles for Firefox. By using Firefox’s Profile Manager, you can manage and edit multiple profiles. The profiles.ini file has a list of profiles, their names, relative paths on disk, and various flags. Each profile is numbered, beginning at zero. When you use Firefox, it loads profile zero by default. The profiles.ini file names profiles as “[Profile0]”, “[Profile1]”, etc. There might be two initial profiles, but there can be more added.
Each profile folder has a randomized name created by Firefox during the first run. The “Path” variable points to the actual location of each profile folder on disk, and the “IsRelative” flag indicates if the value of the “Path” variable is relative to the Profiles folder. It’s possible to set the “IsRelative” flag to 0, then move the profile folder to another location and update the “Path” variable to match. However, moving a profile folder to another volume may cause problems if the volume is unmounted. Firefox will not be able to read the profile folder in that case.
Firefox timestamps each profile folder in the Profiles folder. If there are unused profile folders, you can safely delete them, except for the one indicated in “[Profile0]”. Inside the default profile folder, there are several files and folders used by Firefox. Some are important and should not be removed, while others can be deleted to save disk space. Always save your open pages in Firefox in the Settings window before altering or removing any items in a profile folder.
It’s possible to delete some folders from the profile folder to save disk space. You can experiment to see what the effects are of deleting each. You can also do a total reset for maximum disk space savings. However, this will cause you to lose open tabs, the state of Firefox, cookies, the UI, and other settings. To perform a total Firefox reset, back up some critical files, then delete the entire profile folder. Once you’ve done that, the next time you run Firefox, it will create a new profile folder by default.
After the new default Firefox profile folder is created, restore your original critical files. Once you’ve done that, relaunch Firefox. Everything will be restored as it was originally. If you really want to do a complete Firefox reset, you can delete the entire Firefox folder itself after backing up some critical files. Restoring your backed-up copies to the new default profile folder will restore everything to its original state.
