Good afternoon! We use Thunderbird for our business across several computers. However, on the main computer, we've suddenly received blank tabs at the top of the page, as if an open email thread is there. There are about ten or so of these blank open tabs, and you cannot exit them. The X button doesn't work on them, nor does Ctrl + W. I've uninstalled and reinstalled the software, and we've tried a shutting everything down and restarting the computer, but nothing seems to get rid of the tabs. Is this an issue others have experienced and, if so, what's the best remedy for it? Thanks in advance!