My computer was updated with the lastest Thunderbird version and the screen is blown up out of all proportion

My computer indicated that there were updates to install. I clicked the update button. A whole host of items were updated, including operating system updates. When it was all over, Firefox opened up with an appeal for a donation. I made a donation. When I returned from the donation, I opened up Thunderbird. The screen was so magnified, there was no section where you could see the whole section. Particularly annoying was the return of the "new Thunderbird" which I had suppressed using a Thunderbird app that gave me back the old Thunderbird screen which I knew how to operate. How do I get rid ov the magnification and get my old Thunderbird screen back?

I apologize if I seem grumpy. I wish Mozilla wouldn't change things that don't need changing. Also, I'm 84.