My pop up loading screens never disappear like they normally do. I have noticed other problems like yours too sporadically.

i have this problem in ubuntu 10.10 with gnome 2.32.0. no submenu items can be opened and therefore they are not selectable. main menu items are selectable.

This annoying problem is still happening. Windows did an automatic update to the ATI display driver - made no difference. Windows also installed SP1 patches - made no difference. I run dozens of apps on this computer and Firefox is the only one with drawing problems like this. VERY FRUSTRATING!

The uploaded image shows the Tools menu disappearing, except for the shadow of the dropdown box. The menu still operates - if I click inside it, the proper menu item is selected. Also, if I jiggle the mouse around, the menu contents flicker on and off. This happens for all pop-up and pull-down items - application menu, URL drop-down, right-click menu. Again, only the latest version of Firefox does this, not even the 4.0 beta (which I've since uninstalled).

Interesting data point: I have two monitors, one running VGA, one running DVI-D. The problem occurs on the VGA monitor, but NOT the DVI-D monitor. The monitors are identical. I can move the same window back and forth between the monitors - it'll exhibit the problem on the VGA, but it'll work fine on the DVI-D.

Both my monitors act the same, both are 1920x1200 DVI. I updated the ATI device driver (no difference) and did the Firefox 4.0.1 auto-update (no difference).

It's likely related to some weakness in the ATI display driver, but the strange thing is that it also affects the system menus in FIREFOX ONLY. I have dozens of other programs installed on this i7/Windows 7SP1 computer and this problem suddenly appeared when I upgraded Firefox to 4.0. No problem with 4.0 on my old laptop.

It's definitely related to having the firefox window on your secondary monitor for me. Not ATI related either, as I've got a Nvidia card here.

If I swap my firefox window to my primary monitor, it works properly.

You are quite correct! It fails on the secondary Windows monitor, even though both displays are identical and driven via DVI from a dual-head ATI driver board. A quick test on the primary Windows monitor functions properly.

Incidentally, the "secondary" Windows monitor in my setup is the primary physical monitor.

Same here. VGA + DVI(-D) connected to GTS450 card, DVI works fine. VGA -> menu troubles. Other programs work fine on the VGA display. Running latest 5.0 Firefox.

http://support.mozilla.org/en-US/questions/779732

That fixed my problem