Paul, thanks for posting this.

We are trying to understand what is causing this, so that it can be fixed.

Is that picture taking up the full screen? And on your windows 10 system, have you set screen scaling in your Windows display settings?

Hi Wayne, I am so glad somebody might be able to help me. Yes, that is a screen shot of the entire screen. My Windows 10 display settings are as shown below.

Thanks! Paul

And, to anticipate your next question, when I change the scaling to 100%, there is no change in the appearance of Thunderbird!

Did you restart Window and obviously Thunderbird after the change?

Thunderbird in particular pick up much of into environment information at start, so just changing it without a restart may not be including the change.

I just restarted Windows 10 and Thunderbird with the screen settings at 100% rather than my usual 225%. It had no effect on Thunderbird -- the menus and panels are still grossly oversized. In addition, the Zoom controls (either with ctl-scroll wheel or with Ctl-plus/minus are grayed out / disabled.

Check the Config Editor for this settings:

• Settings > General
• scroll to bottom and click on 'Config Editor' button

It opens in a new tab

• In top search type: pixels
• look for this line : layout.css.devPixelsPerPx
• default is a negative number -1.0

It should not be in bold text, if bold text then it has been altered.

• If you have anything else in that setting use the arrow icon on far right - click on it and the default is reset.

Please post your results.

The setting was in bold at 3.0. It is now back to the default and things look normal again -- many, man y thanks for helping solve this problem. I have no dea how that setting got changed, but now it's back to normal. Again, thanks!!!

User has trouble again in https://support.mozilla.org/en-US/questions/1427106