firefox freeze

Hey,

Does anyone else see problems with firefox  39/40  on slackware 14.0
64bit  that the browser screen freezes?

like youtube, or even news sites streaming, there no certain time
before this happens, sometime,s its less than 1 minute, other times, 4
or 5 or 6 minutes, sometimes 20 minutes, the audios always  fine and
the moment you touch the mouse or tap a key on KB, the frozen image
resumes streaming at the current point in time, I run an ADSB feed
locally and I connect to its http port and same happens there, touch
the mouse again and all hte lil planes appear 50 miles away (where
they actually are at that time)

from all my attempts to reproduce this, its only firefox it seems.

ciao