I recently experienced "severe video stalling" where streaming video would play for 2 seconds and stop for 33 seconds, play for 2 seconds, stop for 33, etc., etc.... I tried everything I could think of: clearing all history, disabling all add-ons, etc. I ended up uninstalling FF, deleting every Mozilla folder, and re-installing. Video plays again--so far, so good.
("Freezing" to me, is when the whole system briefly will not respond. "Stalling" to me, is when only the video stops.)