Since a couple years ago, I had some serious issues with Thunderbird on my company's Win10 notebook. Opening messages in new tabs just created blank tabs, and sometimes, the window got into a state where trying to size it from any border immediately crashed the window. I installed TB on a new machine this morning, and at first, all worked. But after a reboot, I started seeing the same problems on my new machine! After dozens of crashes, changing profiles, safe mode, etc., I was just about to give up, but then I tried to start TB in "Elevated Mode". Our company uses PowerBroker, and starting "Run Elevated" a program gives it higher levels of permissions (not admin but something between user and admin). Voila. All of a sudden, TB is working again as it used to years before. There seems to be either a serious defect in PowerBroker, Windows or TB, but this defect is probably too rare that it'll get fixed. So I hope anyone else using TB and PowerBroker can confirm a similar problem and my solution!