Now I have lost all my saved message folders

Thanks for the screen shot - it is super helpful.

That is a shot of your entire monitor? What is your monitor size? And have you set any scaling or changed DPI in the Windows Display settings?

re : I can't move the line below messages up like I used to so I can't read messages below it.

This has been caused by the developers setting the minimum height to 200px, so you need to use the info at the following link to reduce it. I used 150px, but in your case I suggest you first try 100px. Don't be put off by the instructions as they have helped lots of people. It's not as difficult as it may look. People who may never do into the area mentioned have found it easy to follow.

• https://support.mozilla.org/en-US/questions/1423733

A bug regarding this has been created but no idea how long it will take to get fixed.

re : Everything looks too big.

In addition to the info requested by Wayne, can you provide the following info:

• Menu icon (3 lines) - Font Size - what does it say the size is eg: 12px ?
• Click on the - icon to reduce the font size and tell us what px size works best for you.

In Thunderbird

• Help > Troubleshooting Information
• scroll down to 'Important Modified Preferences'
• Copy all lines that start with 'font.' and paste info into this forum.

> This has been caused by the developers setting the minimum height to 200px,

(This is more for the reporter)

200px does explain why the size of the message list cannot be reduced. But the screen shot (if it is the entire screen) has far too few lines of vertical display for the 200px to be the main issue. Unless the user has a 13" screen.

But your other questions might help.

We have determined that some users somehow have a non-default value for a hidden preference ...

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

Please post your results. Thanks