The short answer
Yes. Rebuilt or re-downloaded automatically when needed.
What is it?
Firefox’s disk cache for each profile: images, scripts and pages from websites you visit, in ~/Library/Caches/Firefox.
What happens if you delete it?
Rebuilt as you browse. Bookmarks, passwords, history and cookies are stored in your profile in Application Support, not here.
How to remove it properly
In Firefox, open Settings › Privacy & Security › Cookies and Site Data › Clear Data… and select only the cached web content option. Or quit Firefox and move the folder to the Trash.
Quit the app that uses it, then move it to the Trash. Empty the Trash when you’re sure.
How MoreRoom helps
MoreRoom recognises this item, shows its real size and when it was last used, and labels it “Safe to remove”. In the free version you can move it to the Trash in one click, with Undo; Pro collects every safe item at once.
Frequently asked questions
Is it safe to delete the Firefox cache on Mac?
Yes. Rebuilt or re-downloaded automatically when needed. Rebuilt as you browse. Bookmarks, passwords, history and cookies are stored in your profile in Application Support, not here.
Will Firefox cache come back after I delete it?
Yes. Rebuilt as you browse. Bookmarks, passwords, history and cookies are stored in your profile in Application Support, not here.
How do I remove Firefox cache properly?
In Firefox, open Settings › Privacy & Security › Cookies and Site Data › Clear Data… and select only the cached web content option. Or quit Firefox and move the folder to the Trash.