I can no longer enjoy it as it is no longer visible; no icon.
It shows up under add-ons, but not in Firefox.
The speeds are also listed on the add-ons page, but are grayed out and can not be edited.
I checked script-block to see if it was blocking it but was told that the page was privileged and could not be edited.
A similar utility works well on Chrome.
Had to reinstall. Now it seems to work...

Can you please add incremental speed?
Can you please add auto speed modifier?
How can we contact the developer?

The most recent update added a button to the Firefox Toolbar. Due to this change, users can't change a video's speed while in full screen.