This can be caused by a corrupted font or by a font that can't be loaded, so you need to find out what font this is about in your case. You can right-click and select "Inspect Element" to open the builtin Inspector with this element selected. *https://developer.mozilla.org/en-US/Tools/Page_Inspector/How_to/Examine_and_edit_HTML 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/Edit_fonts