I was over at Michel V’s site (creator of b2) last night and found some great code for hiding banner ads (images and flash) with Mozilla based browsers like Chimera (for Mac OS X) and Phoenix (for Windows). I extended it just a little, making it block a few more images sizes that I see on Yahoo! a lot. This fix is really nice in that it functionally removes the image from the page ( style="display: none;" ) which means that the rest of the content can move up or over when the ad is gone. Here is the code I’m using:

/* this hides the usual 468x60 Flash banner ads */
embed[type="application/x-shockwave-flash"][width="468"][height="60"] {
  display: none !important;
  visibility: hidden !important;
}
/* this hides the not so usual but very annoying 728x90 Flash banner ads */
embed[type="application/x-shockwave-flash"][width="728"][height="90"] {
  display: none !important;
  visibility: hidden !important;
}
/* adding more conditions to block Yahoo! ads */
embed[type="application/x-shockwave-flash"][width="300"][height="250"] {
  display: none !important;
  visibility: hidden !important;
}
embed[type="application/x-shockwave-flash"][width="120"][height="600"] {
  display: none !important;
  visibility: hidden !important;
}
img[width="468"][height="60"] {
  display: none !important;
  visibility: hidden !important;
}
img[width="728"][height="90"] {
  display: none !important;
  visibility: hidden !important;
}

In Chimera, I created a new file with these contents and saved it here:
/[Your HD Name]/Users/[Your User Name]/Library/Application Support/Chimera/Profiles/Default/[some weird folder name.slt]/chrome/userContent.css

Thanks Michel, very good stuff.