I love Firefox Reader View. But not its fonts. More specifically, these are not the best choices: body.serif, body.serif .remove-button { font-family: Georgia, "Times New Roman", serif; } body.sans-serif, body.sans-serif .remove-button { font-family: Helvetica, Arial, sans-serif; } I'd rather have this: body.serif, body.serif .remove-button { font-family: "Cambria", serif; } body.sans-serif, body.sans-serif .remove-button { font-family: "Open Sans", "Segoe UI", "Tahoma", "Calibri", sans-serif; } Now, I can apply these changes manually every time I open the Reader View via the developers tools. But is there a way to automate this? I tried Stylish, but either I could code it correctly or Stylish wasn't up to the task. Answer In case you haven't gotten around to hunting this down yet, and/or for posterity, as of FF v60 the solution is to: locate your profile folder (listed in about:support ) in there...