Some Extension Messing w/ Firefox

[yellowjack]

I went here: http://music.aol.com/songs/newsongs.adp

And tried to listen to the "Editor's Picks". I downloaded an extension (for Java, I think) and it didn't work, i.e. all play buttons showed the javascript:void,null so I tried on MSN Explorer and it's worked.

Back on Firefox, some webpages aren't displaying correctly. For example, on http://www.fullcontactpoker.com , it shows the menu, the ads, and the blog entries below that across the entire width of the screen. There are no graphics on the webpage except the images of FCP clothing at the Oakley ad. The background is still a plain white.

Did I really f--k up the Mozilla Firefox browser by installing the extension? What do I do?