grease monkey? (firefox) does this thing do anything?

Question

i added it
it's there
i see it
i messed with it

lol
How the hell do i use this?
example
i have a video on youtube i posted(maybe elsewhere)
all this FLV stuff
i deleted it from my computer
i want it back
what do i do

i am way to immpatient to even read stuff at this point but maybe somebody can give me simple instructions or links to where they do so
i can't find anything useful in the 3mins i tried looking

Answer 1

It's a Firefox extension which lets users add bits of DHTML to any web page to change its behaviour.

If you don't need to "add bits of DHTML to any web page", delete the extension from Firefox.

"i want it back, what do i do" - download it from YouTube.