Steps to reproduce: 1. Visit this URL: data:text/html, <a href="http://w.com" title="hello">hi</a> 2. Hover mouse over the link Expected result: "Hello" tooltip appears Actual result: No tooltip appears This bug is reproducible with my main profile as well as a brand new profile. My current work-around is to go to Firefox Menu -> Help -> Restart with Add-ons Disabled... Note: If I choose "Continue in Safe Mode", then the tooltips begin working again. Alternatively, if I check off options and choose "Make changes and restart" then the tooltips will remain broken. I have also disabled all extensions and plug-ins with no success.

BTW, setting gfx.direct2d.disabled to true has fixed this issue for me.