Ever since I've upgraded to Firefox 19 from 18 none of my drop down menus work, they're all completely transparent as you can see in the following screen shot: http://i.imgur.com/PvKyZ6K.png
It's this way in every field in which drop down options appear, including the awesomebar (which is the most annoying).
Try to disable hardware acceleration in Firefox.
Try to disable transparency in Windows.
Right click in a free space on your desktop. Left click on Personalization. There are four options at the bottom of the screen, choose "Window Color and Appearance". Select a border color Uncheck: "Enable transparency"
Thanks but neither remedy worked, nor did several uninstalls & reinstalls. I'm thinking of just going back down to 18 or trying out the beta channel for the 20s.
I really hope there's a solution for 19 out there...
Did you try a clean reinstall?
Do a clean reinstall and delete the Firefox program folder before (re)installing a fresh copy of the current Firefox release.
Download a fresh Firefox copy and save the file to the desktop.
Uninstall your current Firefox version, if possible, to cleanup the Windows registry and settings in security software.
Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.
Your bookmarks and other personal data are stored in the Firefox profile folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.
If you keep having problems then also create a new profile.
Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.
Did you already try a new profile?
See "Creating a profile":
If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.