This likely means that Firefox isn't able to access the requested font locally and falls back to a 'last resort' font that shows all glyphs as a '?' or an 'A'. You can check in the <b>Rules</b> tab in the right panel in the Inspector what font-family is used for selected text. You can check in the <b>Font</b> tab in the right panel in the Inspector what font is actually used because Firefox might be using a different font than specified by the website. *https://developer.mozilla.org/en-US/Tools/Page_Inspector/How_to/Examine_and_edit_HTML *https://developer.mozilla.org/en-US/Tools/Page_Inspector/How_to/View_fonts ---- You can check for sandbox security issues when Firefox has a problem to access fonts installed locally. *https://wiki.mozilla.org/Security/Sandbox You can set this pref to 2 or 1 on the <b>about:config</b> page to reduce the sandbox security level. *security.sandbox.content.level = 1 *close and restart Firefox to make the change effective. If '1' still doesn't have 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. You can open the <b>about:config</b> page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue. *https://support.mozilla.org/en-US/kb/about-config-editor-firefox See also: *https://wiki.mozilla.org/Security/Sandbox#Content_Levels