The Firefox GUI is zoomed out/low resolution. This affects all parts of the browser (buttons, tabs, bars, etc.) and the web pages displayed.
I have tried running in Safe Mode and then reset Firefox; neither fixed the issue.
Note that my display settings are correct, as Firefox appears to be the only application affected.
Go to Solution.
Code changes regarding HiDPI have landed in Firefox 22 and later (bug #844604).
You can modify the layout.css.devPixelsPerPx and increase or decrease the value in 0.1 or 0.05 steps to adjust the size of fonts and other elements in Firefox.
If web pages needs to be adjusted after changing this pref then you can look at the Default FullZoom Level or NoSquint extension.
Use this extension to adjust the font size for the user interface:
Thanks for the quick replies. Too bad Google doesn't have any of those near the top, as it appears to be a common issue.