-
Open
~/.mozilla/firefox/<your_profile>/chrome/userContent.css
(create it if does not exist). -
Paste the following content in it.
@namespace url(http://www.w3.org/1999/xhtml); @-moz-document regexp("chrome://browser/content/devtools/**/.*"){ .devtools-monospace { font-family: Consolas, monospace !important; font-size: 8pt !important; }
}