New circuit display button missing after upgrading to 12.5

I've upgraded from TBB 12.0.7 to 12.5 but I can't see the new circuit display button (and of course the old circuit info in the site information panel is gone).

What I tried so far:

• Disabling a couple of add-ons
• Restarting multiple times
• Resetting the toolbar to the default one (I had customized it)
• Looked at the browser console, but I couldn’t see any relevant messages (can you suggest other debugging tools?)

Other info:

• Platform: Linux.
• The “new circuit for this site” icon works ok as usual, like everything else in TBB.
• Mine is an old installation that has been updated several times with no problems.

I have modified some settings in about:config, but I can’t think of any relevant settings that could prevent the circuit icon from appearing, can you suggest any? Maybe there is a way to backup my current about:config settings, test resetting to the default values, and go back to my settings after the test?