Ubuntu 9.10 Karmic
2.6.31-19-generic-pae i686
Latest Sun-Java-Plugin and the Flashplugin from the Ubuntu-packet flashplugin-nonfree, which should be the latest
Addons in Firefox:
ADBlockPlus
VideoDownloadHelper
VLC/Totem/DivX-Plugins
I'm pretty sure it's a FlashGot-Bug because disabling the other Addons doesn't have any effect, but disabling FlashGot preventing Firefox of crashing like described below.
Bug-Description:
Well, it's a bit hard to explain but I'll try it:
When I try to open a page with java-content with all the above mentioned Addons enabled (an example, a german-chat-room can be found here: http://www.mainfranken-chat.de/zumchat) it works. But, with the java-page still opened in another window/tab and opening youtube Firefox crashes.
The last thing Firefox does is loading the page, the little indicator in the youtube-flash-applet moves to show the loading-progress and stops after about 1-2 sec. and firefox is 'dead'. The last thing firefox shows in the bottom-status area is -translated someting like- "Loading from cache<x>.c.youtube.com" (where <x> is a number).
The problem was in Firefox 3.5 whis was the reason for upgrading to FF 3.6.
Another point which may should be mentioned, the other Addons are for sure not responsible for this bug, with trial-and-error I found out that only disabling Flashgot let the crashes go away. At first I thought the Addon VideoDownloadHelper may be responsible again for this kind of problem (like it was about a year before) but it wasn't.
Okay, I hope you understand what I wrote before, I'm from Germany and my English might isn't as good as you're used to read so please excuse

If you need any more information for resolving this bug please let me now I'll do what I can to get it for you

Thanks in advantance,
BlackVodka