I can only compose email in safe mode. Why? No add ons are listed in my account.

I am running TB 60.0 on a High Sierra Imac. For the past few months when I try to compose or reply to an email I can not compose in the message box. I type, but nothing appears. Same behavior if I try to type an address in the To: box Based on reading other queries with related problems I put TB into safe mode and everything works fine. Before going into Safe mode I looked at the Add-ons list under the Tools tab, but none are listed. So I'm not even sure why Safe mode is making any difference. Also, I tried to have TB always open in Safe mode by checking the box when I go into Safe mode. However, any time I restart TB it opens in normal mode and I have the same composition problem. I saved my Profiles folder and reinstalled TB today, but the same problem persists. How do I fix this?