Sometimes its not a missing font but it is an unsupported character code page for specific characters. A website may be expecting unicode character support rather than standard ASCII characters supported by the default font you have selected in your browser. You may be able to change your browser default font setting to a font which supports more extensive alternate character codes, but since I don't use Firefox I can't help with that. Unfortunately Windows does not make it easy to determine which fonts support extended characters. You have to open the Character Map accessory, select a font, check to see that Unicode is selected and then scroll down the list of characters. Some fonts have more extensive unicode tables than others.