1. I installed the nightly build as told.
2. Open nightly build
3. Went to the "Save Recording" option
4. The first two times, I got a [javascript error] saying I could not record.
5. The remaining couple of times - after I open a "New Recording Tab", whatever that is - I didn't see the javascript error but the website whose clickthru I wanted to record using this tool didn't even load in that new recording tab.
Just this morning I recorded a clickthru like caveman using Quicktime. Can't wait for FF to iron out the kinks in this feature.