Rated 5 out of 5 stars
I have the very same problem hexium posted on June 24, 2012. (If I click 2 times, I'll get 4 repeated entries).
This addon appears to work fine, but since FF13 it doesn't work with the "custom buttons v0.0.5.5" extension anymore.
This is a pity because it always worked fine until now...
There are some steps that can help me to figure the issue out.
1. Restart your Firefox.
2. Ctrl + Shift + J
3. Click Clear button and choose All in Error Console.
4. Click Firefox Button. If the issue occurs, close the menu and click the button again.
5. Copy the errors in Error Console and post them in the discussion forum.