This is weird, but certainly fitting given the original problem: my question was truncated; a lot of details were cut off. So here's the information that was so cleverly removed by the Support software:

But I could not find anything about restoring the profile that Firefox had before it upgraded itself. My hunch is that Firefox somehow screwed up and deleted that file. I looked in Library>Application Support>Firefox and found "profiles.ini", and it was created in 2017, but modified this morning, and is only 375 bytes long. This suggests that Firefox simply removed the contents of my profile and replaced them with a bare-bones profile. I couldn't even access my original Firefox account--I had to create a new account just to get to this page.

There is also two folders inside the Firefox folder: the first was created this morning and has 37.7 MB of contents, but the second has contents going back to 2018 and has 379.1 MB of contents. This appears to be associated with the original profile.

Here are the contents of "profiles.ini":

[InstallAB29A9FE12074BA9] Default=Profiles/es39c72z.default-release Locked=1

[Profile1] Name=default-release IsRelative=1 Path=Profiles/es39c72z.default-release

[Profile0] Name=default IsRelative=1 Path=Profiles/s6sqihjd.default-1531544800420 Default=1

[General] StartWithLastProfile=1 Version=2

[Install2656FF1E876E9973] Default=Profiles/s6sqihjd.default-1531544800420

Now, the first default profile (Profiles/es39c72z.default-release) is the bare-bones profile. But the second entry (Profiles/s6sqihjd.default-1531544800420) is the big one, and I suspect that it is the original. So I'm tempted to just edit profiles.ini to use the path for the original profile. But that's always a tricky business; for all I know, running Firefox with a modified profiles.ini could end up with smoke pouring out of my Mac's ears.

Any thoughts?

'Gadzooks' - I haven't heard that expression for years, so at least you've managed to keep your sense of humour!

I'm not familiar with Mac specifically, but have a look at -

• Recover user data missing after Firefox update.

• Profiles - Where Firefox stores your bookmarks, passwords and other user data.

• Recovering important data from an old profile.

If your question is resolved by this or another answer, please help other users by marking the best reply as Solved. Thank you!

Thanks for the help. Late last night I think I solved it. I went into the profile and did a switcheroo between the two references to the old profile and the new profile. It's a cheat solution, and I'm still not absolutely certain that I haven't screwed things up, but so far, so good.