Reset the page zoom on pages that cause problems. *<b>View > Zoom > Reset</b> (Ctrl+0 (zero); Cmd+0 on Mac) *http://kb.mozillazine.org/Zoom_text_of_web_pages Try to disable hardware acceleration in Firefox. *Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available" *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes *https://hacks.mozilla.org/2010/09/hardware-acceleration/ Try to set the gfx.content.azure.enabled pref to false or if this didn't help disable Direct2D by setting the gfx.direct2d.disabled pref to true on the about:config page and leave hardware acceleration otherwise enabled. *http://kb.mozillazine.org/about:config