What program folder are you referring to? I created a brand new Linux user, logged out of my everyday account, and logged into the new user at the GUI screen. Launching FF in that new user's environment allowed extensions to be installed.

Nothing should be shared.

$HOME/.mozilla/extensions is empty. Where would such a temp directory be located?

What program folder are you referring to?

On the Troubleshooting Information page (Help > More Troubleshooting Information), in the first large table, it's listed under "Application Binary."

$HOME/.mozilla/extensions is empty. Where would such a temp directory be located?

Usually there is an extensions folder in your profile folder after you install the first extension. I don't know whether Firefox uses the system temp directory (or other directory) for the initial XPI file download or downloads it directly into the profile/extensions folder.

I have an extensions directory. It's empty. It appears that FF created the directly but failed to actually use it.

I actually got extensions to load earlier today by umounting my home directory subvol, nuking the account and recreating it. After getting my data directories remounted, I was able to add a couple of extensions but now *that's* not working any more. Even after being able to add a couple of extensions, that subdirectory is *still* empty so I guess it's only used during the actually extension install process and then cleaned up.

BTW, that extension add process is broken on Thunderbird as well. And if you had mail filters? Well, not any more.) IMHO, it sure looks like the Mozilla folks have problems that don't get fixed using the info on their support site. Aggravating to say the least that the application is *this* fragile.

For the record: FF 145.0 (64-bit) I only have a single profile so there shouldn't be any conflict with others.