Rated 3 out of 5 stars

I really like the functionality... Flash simply acts as if it's not installed. Perfect! But as others have reported, I find that the enable/disable button keeps disappearing from the toolbar, pretty much at random. (It doesn't appear in the Customize menu, so it's still 'installed'... it's just not displaying.) I also wish FlashDisable could kill Flash in memory. This would probably be very tough to do, but you need to bear in mind that if you toggle Flash 'Off' after viewing Flash content, the Adobe plug-in will still be running (albeit inaccessible). Even with these limitations, FlashDisable seems to be the best of the Flash-toggle add-ons. If the vanishing-button bug ever gets fixed, I'd eagerly give it a 5 out of 5.

This review is for a previous version of the add-on (0.8.4). 

Thank you for your compliment!
I think cleaning up memory is something firefox or the plugin itself should do and it seams this is already working: If no website is running, the two flash processes (under win64) keep running for some minutes (seems sensible to me, because there is a high probability that you will view more than one flash applet in a row, e.g. while browsing youtube) and then exit.
Concerning the disappearing of the icon: I have tested the addon on several machines with various versions of firefox and have not found anything that could explain this behaviour. If you want, you can contact me via email so we can try to find a solution.