When hitting the minimize button, Firefix wont minize
The window stays on top.
Im using 10.0.2.
Please check if this happens in Safe Mode.
Troubleshooting Extensions and Themes
That was the first thing I tried. It does happen in safe mode too.
Try this : Toggle in FullScreen mode by clicking F11 in keyboard, move the cursor in the up-right area of the window and try to minimize now.