I have tried downloading this a few times and always get this message....Firefox could not install the file at http://releases.mozilla.org/pub/mozilla.org/addons/1865/adblock_plus-1.3.6-fn+tb+fx+sm.xpi because: Signing could not be verified. -260 What does this mean? How do I correct it? I have Win XP I had Adblock Plus until I re-formatted my computer 2 days ago and now can't get it back. I want to get rid of the annoying adds