Hi, this problem is in the separate popup window that says Library in the upper left corner?

You can test in Firefox's Troubleshoot Mode to see what fonts look like with userChrome.css deactivated temporarily: Diagnose Firefox issues using Troubleshoot Mode -- use Open, not Refresh.

If your userChrome.css file uses @-moz-document around rule blocks, it's possible your rules treat the Library window differently than regular browser windows. ??

Thanks jscher2000.

I renamed my userChrome.css file to userChrome.old and it solved the problem ... but it also reverted my bookmark folders to gray which is what the code in the userChrome.css file was supposed to fix and restore the old yellow colour. I copied it from old Win10 computer that I'm retiring and see that the same 'big font problem in Manage Bookmarks is on that computer too.

My laptop also has a userChrome.css file that sets the bookmark folders colour to yellow and the Manage Bookmarks font is fine. I'll look to see how that code differs from what I was using on this computer and use that code instead.

Like so many things, when you don't do something often (like create a userChrome.css file that sets bookmark folders to yellow) you forget how. Use it or lose it ... <g>

Thank you for your help and pointing me in the right direction :-)

R

If you decide to restore the file (keep a backup), you could look for and delete font-size rules so font sizes are not affected.

You can use the Browser Toolbox to check out what rules are applied.

• https://firefox-source-docs.mozilla.org/devtools-user/browser_toolbox/

The left panel in the Library uses treechildren,