This can happen when Firefox has a problem to access locally installed fonts because of sandbox security issues. https://wiki.mozilla.org/Security/Sandbox You can set this pref to 2 or 1 on the about:config page to lower the sandbox security setting. security.sandbox.content.level = 1 Close and restart Firefox to make the change effective. If '1' still doesn't have an effect then try '0' to disable the sandbox. If this didn't work then undo/reverse the change and reset the pref via the right-click context menu to the default value. Type '''about:config'''<enter> in the address bar. If a warning screen comes up, press the '''I Accept the Risk''' button. At the top of the screen is a search bar.