Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I would like Firefox to display XML document trees in a monospace font, instead of using the default proportional serif font.

For a single document I can do this from the menu View->Page Style->Monospace, but it falls back to the default if I reload the document or fetch a new one.

Is there a way to permanently change the font used for rendering XML document trees in Firefox without affecting the way non-XML documents are rendered?

share|improve this question
up vote 4 down vote accepted

Note: The following solution will also affect the View Source browser.

  1. Edit the file C:\Program Files\Mozilla Firefox\res\viewsource.css
  2. Add the line font-family: monospace; to the *|*:root block.
  3. Restart Firefox.

Example (truncated file):

@namespace url(; /* set default namespace to HTML */

*|*:root {
  background-color: white;
  color: black;
  font-family: monospace;
share|improve this answer
Not a very clean solution, but if it's the only way to accomplish what I want, I'll use it. Thanks. – Lars Haugseth Jul 8 '10 at 10:56
By the way, I'm using Ubuntu Lucid, and there the file is located at /usr/lib/firefox-3.6.6/res/viewsource.css. – Lars Haugseth Jul 8 '10 at 10:58
@Lars: Agreed, not a clean solution, but I couldn't think of another way. – grammar31 Jul 8 '10 at 20:25
This solution does not work with Firefox 11 (the file does not exist). Is there another way? – Markus Johnsson Apr 4 '12 at 7:25

There's a Firefox plugin that does exactly that:

share|improve this answer
True, but this feels quite spammy for a plugin that was released 4 days ago and has 6 users. How are you affiliated with this? Are you really David? – Arjan Oct 19 '14 at 9:59

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.