I’ve read countless articles, but I still haven’t found a way to style HTML5 validation errors in Firefox. Has anybody had any luck w/ this? I’ve been able to style some nice messages in Chrome and IE (using Webshims for IE).
I don’t like the look of the messages in Firefox (see screenshot). This link doesn’t sound promising. Nor does this one. However, those links are a bit stale. I’m hoping someone has figured this out for newer versions of Firefox (I’m using version 14.0.1) .

The answer is… there is no answer? I’ve continued searching, and I still don’t see a way to style these errors in Firefox. The good news, however, is that the latest release of Firefox (16.0.1) has cleaned-up the appearance of the prompts, and removed the ugly inner rectangle (see screenshot). Still, it would be nice to style these w/ a custom color; perhaps white text on dark background, for example.