If Thunderbird status bar does not work
You may face this problem with Thunderbird, a status bar that shows at the left bottom corner, only how many messages are unread – no information at all when you connect to your mail accounts, no url when you hover your mouse over a link in a message… If an addon had its icon at the status bar, this also has now disappeared.
Most probably the cause of this trouble to your status bar is an addon.
You have to start disabling one by one your addons, each time restarting Thunderbird, until you locate the addon that causes this problem. In my case it was the “Copy attachment to clipboard” addon.
Thunderbird status bar works fine after I disabled this, but other people report also as problematic addons “Close TAB on Esc”, “Mail Tweak” and “Account Colors”, and there might be more than these.