Devtools using default font rather than monospace

I have my font settings setup as so:

My devtools use the default font rather than the monospace one setup in Advanced settings:

I’ve tried fixing this through userChrome.css but I had no luck. The only “solution” so far is setting the default font to a monospace one, but that affects webpages as well, which is less than ideal.

I am on Arch Linux 5.7.12, using Firefox dev edition 80.0b4 (64-bit), but the issue also appears on my install of regular Firefox 79.0 (64-bit).

Is anyone else experiencing this?


This is tracked in and still being discussed. It makes sense to honor the monospace setting; but needs to be considered in how our designs have to be more flexibe.

I don’t think this is the same as the feature request from

Here it seems that DevTools are picking up the Font set in the Firefox preferences instead of sticking to the default monospace font. I couldn’t reproduce the issue though.

@m.visintin_trenolab did you try using a clean profile?

Thank you for the replies.

I think @jdescottes is right: that bug doesn’t seem to refer to quite describe my issue. I would be happy for the devtools to use any monospace font, but they pick up the default font instead (which by default is a serif font, which isn’t great for looking at code…)

@jdescottes I have tried with a clean profile and with safe mode. Nothing changes.

This is what I can see on U.S. English Firefox 79 on Windows:

Options page > Fonts and Colors section > Advanced button

At the top of the dialog, I choose the Latin character set, then:

(1) Uncheck the box for “Allow pages to choose their own fonts, instead of your selections above” (sets browser.display.use_document_fonts = 0)

(2) Change the Monospace font from Courier New to Comic Sans MS

The tab where I’m using dev tools will switch from using the monospace font specified in the program style sheets to using my specified monospace font, Comic Sans MS.

Note that the relevant character set may vary on other locales.

Is it weird that browser.display.use_document_fonts affects dev tools? Hmm…

You might need rules in userContent.css. You could check for threads on styling devtools on