I have the same problem, and it's annoying me to a degree that makes me consider jumping over to another browser.

I use Firefox on my laptop. When I'm at home, I connect my laptop with an external display. Maximizing the Firefox window (this is not a full-screen issue) on the external display disables the un-hiding of the Windows 10 taskbar which I have set to auto-hide. It works with every single other application and program, but it doesn't work with the one I use the most, Firefox.

Please help us.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Thank you for your reply, Fred. I forgot to mention that I have tried safe mode previously, too, but to no avail. I just tried again -- just in case --, and it did not help me with my issue.

In case I was unclear about this, the issue does not exist when running Firefox on my laptop only, i.e. when my laptop display is my one and thus main display. It only exists when using the bigger desktop display which is then configured to be my primary display, while my laptop display acts as my secondary.