I'm not sure this is actually what worked for me(since it's been a long time since I blocked that thing), but I went hunting around in my Mozilla folders, and in C:\Program Files\Mozilla Firefox\chrome I found a CSS document titled "ads" with the following in it:
Quote:
div.ban,div#ban {
display: none !important;
}
div.ban_bottom,div#ban_bottom {
display: none !important;
}
div.ad_wrapper,div#ad_wrapper {
display: none !important;
Apparently I opened a new Notepad document, pasted that into it, and saved it as "ads.css" instead of creating a UserContent.css file. I'm pretty sure that's what fixed it, but if it doesn't work, try opening all blockable elements with Adblock(shift+ctrl+B) and blocking various elements one at a time--block an item, refresh, unblock if it doesn't get rid of the banner, and move to the next item on the list.
"Oh, better far to live and die/Under the brave black flag I fly/Than play a sanctimonious part/With a pirate head and a pirate heart."