I think that in this case it's easily excusable. It's simply the best possible way to identify text like that.
Well, it is. It can be avoided with "text-decoration: none". Maybe firefox didn't automatically underline abbr when this theme was made? It is a very old theme.
Another annoying thing is that webkit browsers automatically add a colored border around focused inputs, which you have to put "outline: none;" to get rid of.
I feel as though browsers shouldn't assume you want this automatically outlined or underlined like this. It's a problem that developers shouldn't have to take into account.
Same with having to use a titty-ton of different tags for a simple gradient that all accomplish the same thing on different browsers.
-webkit-linear-gradient(red, blue);
-o-linear-gradient(red, blue);
-moz-linear-gradient(red, blue);
linear-gradient(red, blue);
^ that is friggin stupid. the last one should do the same to all browsers, but noooooooo.