On 25.0 and Rated 1 out of 5 stars
Installed, brought up Lightbeam tab, clicked on a few sites, didn't appear to do owt, restarted FF, opened a few sites, still nowt, uninstalled. Mebbe clashing with other extensions?
Oh, and to the Linux fanboi below, this is on Linux...
(I'm loath to give this a rating since there's obviously something getting in the way of its functioning. Couldn't there be a n/a option instead of forcing me to rate this as one star?)