web: How does the browser scale bitmap fonts?

I am wondering if I should avoid bitmap fonts in my web pages. Even if I specify a font size it covers, the user could zoom the page or scale the text.

So - how does the browser scale bitmap fonts?
Should I avoid them in web pages? Or does it suffice to set font-size in points to one of the explicitly supported sizes?
How can I tell if a font is a bitmap font?
How can I tell what sizes are explicitly supported for a bitmap font?

Thanks!