Blef! Finally found a fix for the awesome Tab Mix Plus Firefox extension and the iFox (and associated) themes! Sheesh. Can’t believe I tried to ignore that for so long!!

Follow these steps to fix the problem: - Open a new tab - Type about:config - Create a boolean (Right click » New » Boolean) - Name it: extensions.tabmix.useGreyCloseButton - Set it as false And your problem should be fixed.