Skip the 'about:profiles' part. follow the instructions in the second half here:

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

under "Start the Profile Manager when Firefox is closed". if you're like me, it'll list 'default' and 'default-release'. select 'default' and make sure it's set to use that profile without asking.

that'll take you back to your old profile.

An absolutely horrendously idiotic choice on the part of Mozilla in doing this. Absolutely needless. It's just about pushed me to finally delete firefox after being loyal since about day one, sixteen years ago.

Try to remove compatibility.ini in this profile. You may have to edit prefs.js as well. Note that it isn't recommended to copy a full profile as this can cause issues. Only copy the data files you really need.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

anastrophe said

Skip the 'about:profiles' part. follow the instructions in the second half here: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles under "Start the Profile Manager when Firefox is closed". if you're like me, it'll list 'default' and 'default-release'. select 'default' and make sure it's set to use that profile without asking. that'll take you back to your old profile.

It does not. I did precisely this (well, adapted to my Linux system: launched

./firefox/firefox -P

in my home directory), only to get the exact same warning window mentioned in the initial message ('You've launched an older version of Firefox').

cor-el said

Try to remove compatibility.ini in this profile.

Thank you, but in which profile?

The old one I want to restore or the new one that took over my browser without my permission?

grobber said

anastrophe said

Skip the 'about:profiles' part. follow the instructions in the second half here: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles under "Start the Profile Manager when Firefox is closed". if you're like me, it'll list 'default' and 'default-release'. select 'default' and make sure it's set to use that profile without asking. that'll take you back to your old profile.

It does not. I did precisely this (well, adapted to my Linux system: launched

./firefox/firefox -P

in my home directory), only to get the exact same warning window mentioned in the initial message ('You've launched an older version of Firefox').

So, according to this: http://kb.mozillazine.org/Installation_directory Your new firefox installation may be installed as /usr/lib/firefox-<version> or /usr/lib64/firefox-<version>

Try running that with the '-P' flag - maybe?

and according to this: https://www.howtogeek.com/255587/how-to-find-your-firefox-profile-folder-on-windows-mac-and-linux/

Your profile should be under /home/<username>/.mozilla/firefox/xxxxxxxx.default

Might require running the new FF with the -P then drilling over to the profile dir. Not sure. I use linux constantly, every day, but not on the desktop, just servers - so my desktop skills are weak.

oh, addendum - be sure and make a copy of that profile folder first. A simple

cp -a /home/<username>/.mozilla/firefox/xxxxxxxx.default /home/<username>/.mozilla/firefox/xxxxxxxx.default.bak or .safe or whatever should do the trick.

anastrophe said

So, according to this: http://kb.mozillazine.org/Installation_directory Your new firefox installation may be installed as /usr/lib/firefox-<version> or /usr/lib64/firefox-<version> Try running that with the '-P' flag - maybe?

Well, it's directly <HOME>/firefox for me because I installed the program directly, not through my Linux distro's package manager.

And that's precisely what I did: ran that executable (<HOME>/firefox/firefox) with the -P flag, thus opening the profile manager.

and according to this: https://www.howtogeek.com/255587/how-to-find-your-firefox-profile-folder-on-windows-mac-and-linux/ Your profile should be under /home/<username>/.mozilla/firefox/xxxxxxxx.default Might require running the new FF with the -P then drilling over to the profile dir. Not sure. I use linux constantly, every day, but not on the desktop, just servers - so my desktop skills are weak. oh, addendum - be sure and make a copy of that profile folder first. A simple cp -a /home/<username>/.mozilla/firefox/xxxxxxxx.default /home/<username>/.mozilla/firefox/xxxxxxxx.default.bak or .safe or whatever should do the trick.

I know where the profile folder is: exactly as you describe, in the <HOME>/.mozilla/firefox folder. That's where I've been keeping my preferred profile, syncing it between computers with rsync (drawing from a copy of it I keep in cloud storage, which all of my computers have access to).

If I simply copy its contents on top of whatever other profiles I have I get the same warning window and the two options I'm not interested in ('create new profile' and 'quit').

The same thing happens if I set my preferred profile as 'default' or try to open it in a new window, etc. There's simply no apparent way to get Mozilla to accept running it.

cor-el said

Try to remove compatibility.ini in this profile.

Just reporting back that this worked. There was no need to fiddle with prefs.js in any way. Simply removing compatibility.ini from the old profile I wanted back and setting that profile as default in about:profiles resulted in it restarting without the nagging window.

Thank you!