1. At Firefox, right click on the UI, choose "Customize"
2. Look at the bottom left, uncheck title bar.
Note: it doesn't matter what compositing engine you use. Other applications don't have this problem.
Also, the reason I didn't submit a bug to Mozilla is that KDE doesn't have this problem. It semes to be Mate only. (However, I can't be sure as I haven't tried all possible DEs).
Reproduction steps:
1. At Firefox, right click on the UI, choose "Customize"
2. Look at the bottom left, uncheck title bar.
Note: it doesn't matter what compositing engine you use. Other applications don't have this problem.
Also, the reason I didn't submit a bug to Mozilla is that KDE doesn't have this problem. It semes to be Mate only. (However, I can't be sure as I haven't tried all possible DEs).
Thanks.