Unfortunately, this add-on is no longer able to completely and strictly block all pop-ups (like it used to). This is because of a Firefox change in new versions. I have emailed the developer of this add-on about the issue specifically, but as yet the issue remains unsolved.
This thing means f#[k!n' business!! I can't even remember the last time I saw something that, not only does what it claims, but does so immediately and w/ absolute intent. Tnx for making something that actually works.