How to change the Font Size in Thunderbird

For a long time it has been almost impossible to change the default font-size in Thunderbird. The font is by default very small, and for many of us it has been nearly impossible to read text in ThunderBird UI…

There has been a plugin around for years called Theme Font & Size Changer. But it does’nt work anymore. After Thunderbird version 62 it has not been supported.

So how do you get larger font size in Thunderbird. Here is how to do it without any plugin:

  • Open Thunderbird
  • Go to Help | Troubleshooting Information (Hjælp | Teknisk Information)
  • Scroll down
  • Hit the button ‘Open Folder’. The socalled profile folder opens.
  • Close Thunderbird
  • In this Profile-folder create a folder with the name ‘chrome’ (exact name)
  • In the ‘chrome’-folder create a css file with the name ‘userChrome.css’
  • Paste this code into the file and save it.@namespace url(“”);* { font-size: 15px !important; }
  • Start Thunderbird again

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