There's a difference between not being a designer and just not bothering learning. I'm not a designer either, I suck at designing. Doesn't mean I can't learn how to write proper markup.
Infact, it's incredibly easy. Read up on
this and
this.
If I come over like a twat, it's purely because I'm getting very, very sick of people trying to do things without even bothering to learn anything about what they're doing.
I can understand you're busy, but it really takes only a few hours to make a basic website properly if you learn it. You'll spend alot less time than if you keep copying things from various places.
Oh, and about the plugin. Firefox should alert you if a plugin isn't installed.