Possible false positive Rated 4 out of 5 stars
Please check https://my.bitdefender.com/dashboard - addon says this site is vulnerable while numerous other online heartbleed test services says it's ok.
Good! Rated 5 out of 5 stars
This is definitely the best add-on for Heartbleed checking, as it does everything locally, sending nothing out (if the version notes are to be believed).
Works well with good notification pop-up Rated 3 out of 5 stars
However the Heartbleed checker you use at http://heartbleed.prod.mozaws.net/bleed/ seems rather slow to respond whereas Filippo Valsorda's own checker at http://bleed-1161785939.us-east-1.elb.amazonaws.com/bleed/ seems to respond instantly. Not really any fault of this extension, just something I noticed.