Try to disable hardware acceleration in Firefox.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

• https://hacks.mozilla.org/2010/09/hardware-acceleration/

• https://support.mozilla.org/kb/how-do-i-upgrade-my-graphics-drivers

Thank you. I appreciate the suggestion and have just tried it. Disabling hardware acceleration hasn't solved it, however.

Did you check for problematic extensions and plugins?

Start Firefox in Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes
• https://support.mozilla.org/kb/Troubleshooting+plugins

Thank you but nothing changed when I worked through this. There's got to be something else needed to fix the problem.

So it still happens if you've disabled all plugin and extension and hardware acceleration?

You can try to create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

• https://support.mozilla.org/kb/Basic+Troubleshooting#w_8-make-a-new-profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If the new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

See:

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Does it make any difference if you use keyboard navigation rather than mouse navigation? For example, tab to the control, press Alt+downarrow to drop the list, move the selection bar up and down using the arrow keys, then tab away to accept the selection.

Thanks for the suggestion. That was one of the first alternatives I tried but it doesn't make any difference. I appreciate the help being offered by both of you.

Do a clean (re)install and delete the Firefox program folder (C:\Program Files\Mozilla Firefox\).

Download a fresh Firefox copy and save the file to the desktop.

• Firefox 13.0.x: http://www.mozilla.org/en-US/firefox/all.html

Uninstall your current Firefox version, if possible.

• Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you will also lose your personal data like bookmarks and passwords from profiles of other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your bookmarks and other profile data are stored elsewhere in the Firefox Profile Folder and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

Thank you. I have now tried this - twice! I now suspect that the problem may lie somewhere other than in Firefox but I have no idea as to where that 'somewhere" may be!

You can try to boot the computer in Safe mode with network support (press F8 on the boot screen) as a test to see if that works better.

Thank you. The drop boxes are now working fine on the Menu Bar but they are still not working on drop downs that come with options when completing on-line forms - things such as country, state, etc. Also I cannot use the mouse or arrows to move down options or even control my sound volume.

Hi spaaks, when this happens, does the focus move away from the control? In other words, if you were to press Alt+downarrow again, would the list again flash open and shut, or has the focus moved elsewhere on the page or in the UI?

Do you use any form-filling software such as Roboform?

Have you investigated whether you might have any screen or keyboard recorders (spyware) running?

i'm having the same problem. started about a week ago (7/7/12). i'm on MAC. tried downloading most recent DMG file from website and it still is exhibiting the same behavior. restarted computer. still not working.

Yes, it just flashes again. No, I don't use any form filling software. Yes, I've checked and rechecked - including getting Norton to do a deep clean for me - to try and eliminate any spyware. I have also uninstalled Mozilla, done a complete disc clean and a further virus/spyware check using both normal and safe modes, then restarted the computer and reinstalled Mozilla. The problem persists.

I am very appreciative of the time taken by all of you to help me try and find a solution.