Rated 5 out of 5 stars
Having switched over from Adblock Plus I have to say this addon is pretty unobtrusive. I haven't had to tweak anything really except the aforementioned Yahoo Mail and added a rule for zillowstatic.com when I was browsing there once but all in all it's not caused me any problems. I prefer this a lot over adblock plus simply because it doesn't really need to queue up a black/white list of much so it ideally doesn't need much updating nor overhead on the browser.This review is for a previous version of the add-on (0.4.6.1-signed).
Rated 3 out of 5 stars
name="Whitelist: Yahoo Mail"
it's totally a heuristic filtering app. You need to put in your own customizations if some site you like deviates from an acceptable norm. Use the monitor option to see what happens when you go to a site like mail.yahoo.com & it shows what rules fire off and why it was scored to be a blockable url.
documentation on rules is here http://trac.arantius.com/wiki/Support/KarmaBlocker/Configuration
you can also compare to other rules in the configuration for help.