NoScript Extension
Sometimes, I use a 64-bit operating system (Slamd64, that is), and there is no good Flash option for me. Flash and Shockwave are usually unneeded distractions, so I don't mind.
Alas, sometimes I visit a webpage that features the hated Flash. The Flashblock extension largely solves the problem, but I do sometimes have to tell the browser not to download Shockwave or whatever else I don't (can't) have.
So I got greedy, and I tried to install NoScript, which I knew worked well on Firefox, and thereby prevent those annoying dialogs in Seamonkey
Uh, no. Had to clean out all of my Mozilla settings (in .mozilla/) to get Seamonkey working again at all. Now I am back to annoying dialogs that I can never satisfy, plus I've lost my installed extensions and whatnot. *Pthbbttt*