General background info which might work for you:

In Windows 10 , 'Settings' > 'Ease of Access', there is 'Automatically hide scrollbars in Windows' option - it might be switched on, so switch it off. This should also force the Firefox browser scrollbars to stay visible. But that is a general Windows OS setting.

Also check the 'Registry Editor' - In windows bottom serch type: Registry Select: 'Registry Editor' You may asked permission to proceed. Navigate to this location: Computer\HKEY_CURRENT_USER\Control Panel\Desktop\WindowMetrics

Look for these two lines: 'ScrollHeight' and 'ScrollWidth', By default, they may have this negative number: -252 I had the scrollwidth and scrollheight set to: -255

To alter a number: Double click on the word 'ScrollHeight' and it opens a small window. It will say 'Value data:' and this is where you remove the contents and then type in a suitable negative number. You might need to enter: -255 or if you already see a number simlilar to that try something larger such as: -360 Then click on 'OK' Whatever you set for ScrollHeight', you need to also set up for 'ScrollWidth'.

But in Thunderbird, you may want to set this up with specific control: In Thunderbird.

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

It opens in a new tab

• In top search area type: scrollbar.
• Look for the following 3 lines (as numbered below) and edit them.

1. 'widget.non-native-theme.scrollbar.size.override' - change number to eg: 50 (you can modify this a suitable size ) 2. 'widget.non-native-theme.scrollbar.style' - change number to 4 3. 'widget.non-native-theme.win.scrollbar.use-system-size' - toggle to say 'false'

• To edit a number click on the 'pencil' icon
• Change number and then click on the 'tick' icon to save
• To toggle from true to false - clickon the far right toggle icon

Once you have those three set up, you can then alter the first one to find a suitable size. On my computer 20 was ok, but it all depends upon what screen resolution and scaling you are using.

Hopefully you will find this info useful.

1. 'widget.non-native-theme.scrollbar.size.override' - change number to eg: 50 (you can modify this a suitable size ) 2. 'widget.non-native-theme.scrollbar.style' - change number to 4 3. 'widget.non-native-theme.win.scrollbar.use-system-size' - toggle to say 'false'

I liked 35, style 3, false to fatten scrollbar for email preview box which sometimes goes too skinny and small, on some emails, without getting too large for folder and listing scrollbars. This is on Windows 10 and 4K screen. thanks for info!