Usually adverts on web pages don't irritate me. I know some people hate them, and use blockers to prevent them, but they don't bug me.
Except those stupid, moronic, noisy smiley adverts which some GIT has decided should use sound without asking you first. IDIOTS!
It's especially galling when you're trying to watch (and listen) to a video, so you can't even switch to mute.
To kill them (and I have), edit the “hosts” file. On Windows this is at C:\windows\system32\drivers\etc\hosts or thereabouts. Note the file has no file extension. On a Mac, this Apple support article explains how to get at it.
Put the ad servers you want to block in there, against the loopback IP address of 127.0.0.1. In Firefox you can find them by going to Tools / Page Info / Media and look for the embedded SWF files that match the irritating ads. Use a tab character between the IP address and the server name.
Done. Stupid moronic noisy smiley ads gone.