TOPIC: SUBSTACK
Blocking thin scrollbar styles in Thunderbird on Linux Mint
23rd February 2026
When you get a long email, you need to see your reading progress as you work your way through it. Then, the last thing that you need is to have someone specifying narrow scrollbars in the message HTML like this:
<html style="scrollbar-width: thin;">
This is what I with an email newsletter on AI Governance sent to me via Substack. Thankfully, that behaviour can be disabled in Thunderbird. While my experience was on Linux Mint, the same fix may work elsewhere. The first step is to navigate the menus to where you can alter the settings: "Hamburger Menu" > Settings > Scroll to the bottom > Click on the Config Editor button.
In the screen that opens, enter layout.css.scrollbar-width-thin.disabled in the search and press the return key. Should you get an entry (and I did), click on the arrows button to the right to change the default value of False to True. Should your search be fruitless, right click anywhere to get a context menu where you can click on New and then Boolean to create an entry for layout.css.scrollbar-width-thin.disabled, which you then set to True. Whichever way you have accomplished the task, restarting Thunderbird ensures that the setting applies.
If the default scrollbar thickness in Thunderbird is not to your liking, returning to the Config Editor will address that. Here, you need to search for or create widget.non-native-theme.scrollbar.size.override. Since this takes a numeric value, pick the appropriate type if you are creating a new entry. Since that was not needed in my case, I pressed the edit button, chose a larger number and clicked on the tick mark button to confirm it. The effect was seen straight and all was how I wanted it.
In the off chance that the above does not work for you, there is one more thing that you can try, and this is specific to Linux. It sends you to the command line, where you issue this command:
gsettings get org.gnome.desktop.interface overlay-scrolling
Should that return a value of true, follow the with this command to change the setting to false:
gsettings set org.gnome.desktop.interface overlay-scrolling false
After that, you need to log off and back on again for the update to take effect. Since I had no recourse to that, it may be the same for you too.