Upgraded to 60.2.1 last night OS Windows 7 Pro 64 bit With Aero transparency The problem is that the activity bar is set to be transparent. If Thunderbird is on top of something dark colored you can't read items displaying in the activity bar. Example: I get a message with a suspect URL, I mouse over the URL in the message body and check the activity bar to see what URL is displayed. With a dark background I can't read it. So I open up a blank tab in Firefox and use that as a background, now I can read it. I shouldn't have to turn off Aero nor should I have to edit a .css file or get a theme add-on to pick a readable background color.