YouTube problem

so for some time now i got this problem with youtube...

everytime i want to watch a video directly on youtube it says: "An error occurred, please try again later."
this doesn't happen with embedded videos...i can watch them without any problems.

also to watch any videos at all on youtube, i had to click "open in new window" then it worked.
but now with the new update, it seems like there isnt any option like the "open in new window"-button...so i am searching for your help. :(

any advices? or somebody had the same problem?

things i tried before:

adobe flashplayer update
firefox update
java update (got no clue if its even necessary :p)

thanks in advance.