Trying to adjust CSS in Thunderbird interface, but not taking in Linux version?

Since the Theme Font and Size Changer Add-on is no longer good, and isn’t supported by the Linux version (78), I’m trying to add the userChrome.css file in a Chrome folder inside the profile folder, as per many sites’ explanations how to do so. I’ve also tried editing the layout.css.devPixelsPerPx config file per others’ recommendations but neither are working. Is this a Linux issue since neither is working? The latter config modification actually changes the size of the icons next to the left panel text but not the font,

Has anyone else had this problem? I’m on a new Linux Mint install, three days old, if that helps.

Hey @DavidBorrink!

I have an array of questions:

  1. Have you done this successfully before?
  2. Is the font you’re trying to use in your Fonts folder? You may have to direct the CSS to the correct file path in order for the code to see it.
  3. Have you fully updated your system recently?


  1. No I haven’t done this successfully before, but I do web development so I understand what CSS has to do. Their instructions say to place the userChrome.css file in a “chrome” folder in the profile folder. I’ve done that, then restarted Thunderbird. No change. There are two profile-like folders in the ~/.thunderbird folder and I’ve tried putting them in both locations. No change.

I’ve done config edits before in Thunderbird, so I know what they’re asking. Examples that people have shared show exactly where to go and what to do. I try that and all I get are thicker icons next to the folder list names.

  1. I’m not trying any fonts at the moment, I’m only trying the font size change. That’s more important than anything right now.

  2. This is a brand new installation using the latest release of Mint Cinnamon. Just installed it this week. We have run updates once or twice.

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This styling issue is a major reason I cant use Thunderbird. I have no solutions, just sharing your pain. :sweat_smile:

@DavidBorrink - I also have HTML and CSS experience. I am also running a customized version of Mint Cinnamon that I have tweaked. Having said that, I have not tried to change font sizes before. I usually just do that through the System Settings.

My only thought at this point would be to try and adjust other sections of the Thunderbird CSS and see what happens.

Stupid question: Have you tried changing the font size in Thunderbird’s Preferences? As an additional thought, those settings could be overriding the changes you’re trying to make in the CSS.

My wife’s laptop is where this is happening. She played around and found the System settings area and that did some changes, though I have to say I’m surprised that the Linux system settings could change that. Thunderbird has it’s own look and size and I would think it was independent of platform settings.

Anyway, she got things looking a little better, imported the add-on to restore the color icons (what where they thinking getting rid of those?) and added a theme to give the app a little color.

That’s what confused me: that the Thunderbird userChrome.css file wasn’t doing anything to the system. As someone who regular does CSS tricks with sites, this should have been “101” level changes that work.

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