CodeBurner is a Firefox add-on that integrates with Firebug, to extend it with reference material for HTML and CSS.
https://addons.mozilla.org/en-US/firefox/addon/10273
It is a nice quick way of checking browser compatibility. You can then follow up at the sitepoint website to read more specific info about any issue raised and see if there are any workarounds.
Looks like this:
