It seems like a better question to ask is:
Why is there a fontfamily tag at all?
Do we need a tag for every CSS attribute? Why doesn't css cover it? I see a few misguided tagging attempts in the question list for fonttamily:
fontfamily, fontsize, li, dropdownlist, font-face, pre, dropdown-menu
And these are just the ones that intersect with fontfamily: there seems to be a tag for nearly every single CSS selector, HTML element, and UI control. They should all just go away: tagging is meant to categorize questions into useful segments so people can follow them, not to make sure keywords show up on the question. That's what the question body is for.
So instead of using fontfamily or font-family because you happen to use the attribute in your question, just use css and add any other tag you think a reasonable person interested in answering your question would follow: maybe fonts if it's specifically a font problem.