I tripped across this.
Of course, I'd prefer you download my PAC file for blocking ads:
http://www.schooner.com/~loverso/no-ads/ Sheryl did include this link in the article, but my PAC file has lots of instructions.
The adblock extension for Mozilla and Firefox is an excellent thing to use. If you JUST use Mozilla and Firefox, then a PAC file like no-ads.pac isn't any better than adblock.
However, a PAC file like no-ads.pac gives you something adblock can't: a mechanism that works with other browsers, like E, Opera, Konquorer, etc.
no-ads.pac works perfectly fine with Firefox. (I'm typing this from Firefox now). It isn't really hard to install or understand; try reading my page above. I also have a forum for helping people get started.
The registry setting for IE is needed to stop IE from accidentally defeating a special PAC file. The setting is simple (and the key is listed on my page). You don't need to go into the Internet Properties Advanced settings once you use the supplied .reg file; it defaults to the correct value.
Once you get no-ads.pac working, all banner ads turn into failed image fetches. Under IE, these become a little red "x", or a "broken" icon in Mozilla.
A 'blackhole proxy' is used to serve up a blank image for each banner ad blocked, which makes the red 'x' or "broken" image go disappear.