Not for me. I can slam the cursor to the top edge of the screen and click on a background tab and it comes to focus just fine. This is of course with Firefox maximised. Am on Windows 10 just for info... perhaps the UI is slightly different under your OS...
I'm on Windows 10, too, so I assume the UI shouldn't be that far off.
The problem - see the link to Bugzilla I pasted - is supposedly related to the use of multiple displays (which involves different DPI settings). A small thing to be sure, but somewhat annoying, given that switching tabs is a fairly common action when using a web browser.
What's unpleasant is how long it takes to resolve it. From Bugzilla:
> This is a pretty annoying usability regression that will ship in 50. Will we be able to fix it for 51?
