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).
This is tracked in https://bugzilla.mozilla.org/show_bug.cgi?id=1559152 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.
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.
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…