Ever since I purged kubuntu-desktop from my ubuntu installation, my firefox menu bar text changed to black. I now have trouble using firefox with the ambiance theme.
Is there a package or something that may need to be adjusted?
Go into the chrome folder in your profile, it is ~/.mozilla/firefox/rf1v5r52.default/chrome for me. Then edit the userChrome.css file, where a line was added by QtCurve. I remove that line and Firefox looks just fine.
Try creating a new Firefox profile and test if you still have wrongly coloured menus.
If it doesn't help, the problem might be in your Firefox or Ambianceinstall; open synaptic and mark firefox, ubuntu-desktop (or -netbook if you use UNE), light-themes (includes Ambiance and Radiance) and xul-ext-ubufox for reinstall. Hit apply changes, when done, log out and login back to ensure that any change to the themes configuration is loaded.