Firefox on a Mac: old profiles are usually the reason it is large
Firefox keeps a folder per profile and never removes the old ones. Where they are, how to tell which is live, and what clearing the cache actually does.
Firefox splits its storage in a way that catches people out: the profile and the cache are in two different folders under two different roots, and neither is inside the application. Clearing the cache in Settings empties one of them and leaves the other alone.
The two folders
~/Library/Application Support/Firefox/Profilesholds the profile itself: bookmarks, history, extensions, saved logins, and site storage such as IndexedDB.~/Library/Caches/Firefox/Profilesholds the disk cache, the part that is genuinely disposable.
du -sh ~/Library/Application\ Support/Firefox/Profiles/* \
~/Library/Caches/Firefox/Profiles/* 2>/dev/null | sort -hRead that output for count as much as for size. Most people have more profile folders than they have ever created, because a reinstall, a refresh or a channel change makes a new one and leaves the old one in place forever.
Telling which profile is the live one
Type about:profiles into the address bar. Every profile is listed with its folder path, and the one in use says so. Anything in the Profiles folder that is not listed there, or is listed but has not been used in years, is an orphan you can remove.
Do not guess from the folder names. They are random strings followed by a label, and the labels repeat, which is exactly why this ends up as a stack of folders nobody dares touch.
What is large inside a profile
| Inside the profile | What it is | Safe to remove |
|---|---|---|
storage/default | Site data: IndexedDB, service workers | Yes, but web apps lose offline state |
places.sqlite | History and bookmarks | No |
extensions | Installed add ons | Only by uninstalling them |
sessionstore-backups | Recovery copies of open tabs | Yes, you lose tab recovery |
The usual answer to a large profile is storage/default, which is site storage rather than cache, and is not cleared by clearing the cache. In Firefox that is Settings, Privacy and Security, Cookies and Site Data, Manage Data, where it is listed per site with sizes.
Doing it in the right order
- Quit Firefox. A running browser rewrites these folders as you work.
- Open
about:profilesand note the live profile path. - Remove profile folders that no longer appear there, to the Trash rather than permanently.
- Clear site data per site in Settings for anything still large.
If you use more than one browser, total them all before deciding which to attack. Chrome measured 8.1 GB on a real Mac, most of it profiles rather than cache, which is the same pattern as this page describes. Safari's storage splits into four places again.
Common questions
Where is the Firefox profile folder on a Mac?
In ~/Library/Application Support/Firefox/Profiles, with a separate cache folder at ~/Library/Caches/Firefox/Profiles. Typing about:profiles in the address bar lists every profile with its exact path and marks the one currently in use.
Why does Firefox have several profile folders?
Because reinstalling, refreshing or switching Firefox channels creates a new profile and leaves the previous one on disk. Nothing removes them, so a Mac that has had Firefox for years often has several, each holding its own history, extensions and site data.
Does clearing the Firefox cache free much space?
Usually less than expected. The cache is bounded, while site storage under storage/default in the profile is not, and clearing the cache does not touch it. Site data is cleared per site in Settings, Privacy and Security, Manage Data.
Is it safe to delete an old Firefox profile?
Yes, provided it is not the live one. Check about:profiles for the profile currently in use, and move anything else to the Trash rather than deleting it, since an old profile can still hold bookmarks or logins you have not copied over.