Worked fine for me for a while now Rated 5 out of 5 stars
I've been using this extension since 1.5 and I don't have the white space issues described. Never have.
The only improvement I'd suggest is the ability to add a domain without an A record. Instead of only being able to add addons.mozilla.org here, I'd like to also be able to add mozilla.org to cover everything at this domain.