There's a newish FF add-on called Collusion.
It looks and behaves just like Dimes
http://collusion.toolness.org/

If you don't have it installed, click on the link, after a few seconds some text appears on the left and click on the demo link.

Grab the grey dot with you mouse pointer and drag it around a bit.
Now do the same with a red dot.

Recognize this?

... works and behaves just like Dimes.