Doesn't sound like a firmware problem. Sounds more like a badly authored disc/lens problem.
Check the discs your playing make sure theres no resdue, jam from little critters etc. on em

even the smallest bit of stuff on your disc can affect playback on some players. Also check em for scratches or anomolies on the disc.
If the discs are ok then also try a lens cleaner on your machine, when was the last time you used one or had the player serviced?
Effectively a dvd player is not too disimilar to a vcr. The play head (laser) can pick up dirt. Only difference from vcr is when the lens gets toooo dirty you can't whip the top off and give it a good clean. Instead you end up forking out £75+ for a new laser.... Cheaper method of cleaning works better for the wallet!
BTW if you're playing non original material then ignore what i've said above ...coz as they say "you get what you pay for"