I was having trouble in firefox 3 where flv videos would load up to a certain point and then just suddenly stop loading. It was happpening at around the 5 to 7 minute point of any longer video. (maybe based on loading time?)
The loading progress bar would smoothly fill up and then suddenly shoot up to 100% at the point the loading stopped. When playing the video it would just stop at that point as well.
This is probably not a bug in the player, but I narrowed it down to having the firebug add on installed and enabled in firefox. Just disabling it fixes the issue.
I couldn't find anything in my searches while trying to figure this out so I figured I would make a post just to point it out in case anyone else was having the same issue.
Problem happened with JW player 4.3.132 and 3.99 and firefox 3.5 with firebug 1.3.0 and tested it on 2 different machines.

Thanks for narrowing that down to Firebug -- I've been having the same issue and I never would have figured that part out. But for me it's not necessarily length in time. If i have a very high bitrate video that's only 2 minutes long it cuts off too. I want to say it happens around the 20 megabyte mark but I could be mistaken.