tab switching in Firefox
 

How do you switch tabs in Firefox? I thought it was Ctrl-Tab, as in Windows Firefox, but that apparently switches between desktops. I can't find it in the control center keyboard shortcuts list.

You problem is that you have a global shortcut overriding firefox shortcuts. You need to find the global shortcut in your Windows manager and change it to something else. Alternatively, you can disable global shortcuts for firefox. I wouldn't recommend this for apps like firefox, but it might be a useful solution for things like VMplayer or rdesktop that need those shortcuts for something else.