We have seen reports that this can be caused by a problem with fonts like Helvetica that you have installed locally and that might be corrupted or are missing variants. You can right-click and select "Inspect Element" to open the built-in Inspector with this element selected. *https://developer.mozilla.org/en-US/docs/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/docs/Tools/Page_Inspector/How_to/Edit_fonts

See: *https://support.mozilla.org/en-US/search?w=2&product=firefox&q=field%3Acontent%3A%7Bhelvetica%7D+range%3Aquestion_created%3Agte%3Anow-30d%2Fd