So you might know that /Applications/Firefox.app/Contents/MacOS/firefox-bin --ProfileManager will launch Firefox’s profile manager. Ran into a bit of a surprise when I couldn’t get the profile manager to open, even by deleting profiles/prefs and caches (using Maintenance.app) plus doing other normal fixes.

Despite Terminal reporting “Error: Access was denied while trying to open files in your profile directory.” the actual problem was the Caches directory in ~/Library/Caches – instead of the client’s short username, root owned the Caches folder. Really surprised this guy wasn’t having more issues.

Thought I’d post this here in case someone else runs into what seems to be a profile folder problem but can’t fix it through the usual Firefox-specific methods. In case that doesn’t tell you all you need to know, check this link for more details, specifically the part surrounding the command you’ll use to fix it which I’ll quote here in case it helps:
sudo chown -R `id -un`:`id -gn` ~/Library/Caches
Please note I haven’t tested that on Yosemite 10.10.5 but the code doesn’t look tricky so it should work fine. It’s just a basic chown command with a couple nested commands that insert your specific username and groupname into the main command. Email me at firefoxprofiles at this domain name if you have questions!