I have come across some people who experienced oversized pop windows for various things being too large and checking the following settings are using the default sorted out the problem. See if this is effecting you.

Please check the following:

• Settings > General
• scroll down to bottom
• click the 'Config editor' button
• It opens in a new tab
• In search type: perpx
• look for: layout.css.devPixelsPerPx
• default has negative number -1.0 setting
• click on the pencil icon
• Remove the current setting and type : -1.0
• click on the tick icon to save.

Restart Thunderbird

Hi

That did solve the problem with that and my ongoing problem with the Create filter box being oversized too but now all the text on screen is very small and so rather hard to read, can you suggest anything to help there? Or should I submit a new question for that? Thanks

Just found the Font size setting and that's made it much easier to read...

Just found the Font size setting and that's made it much easier to read...

Just in case anyone else needs to know where to locate the 'Font Size' which helps with Folder Pane, Message Lists. Menus etc

Menu app icon (3 lines) > 'Font Size' > click on the '+' icon to increase font size.

Good to hear the info sorted out the original issue. Could you be so kind as to mark my comment https://support.mozilla.org/en-US/questions/1525097#answer-1751572 as the Chosen Solution so that others with similar issue can locate the info more quickly. Many thanks.