Firefox crashes when I load any youtube video on the latest version, it not only crashes firefox but my whole computer goes blank and I have to restart, why is this?

Question

Backstory: There are two possible events that could be causing this
1: At some point I may have followed a ''Tinyurl' link that consquently lead me to a youtube video, to which youtube worked perfectly fine before hand, and this is where i witnessed the first crash. Theories into whether this link, previously stated, may have done something to my system have been thought about, but the fact that youtube still works on the latest Microsoft Internet Explorer seems to present the idea of a virus or an error redundant. I own the latest Macfee antivirus software and Ccleaner(running the registry check) and have run them complete with disc defragment and scan disc error recovery along with an additional malware scanner. Nothing seems to have come up on anything. After doing all this, my last resort was System restore and this seemed to solve the problem, mainly because i had an earlier version of firefox. therefore i resisted updating for aslong as possible whenever it told me to update. but the otherday i thought i'd risk it again thinking it may have been a problem alot of people have been having and it would of been fixed, but sadly it hasn't. this lead me to google the problem and was advised to start firefox on 'safe mode' as there may have been a confliction between add ons or plugins with youtube or some thing like that, but sadly that hasn't worked either. The plugins i had installed with it were the ones firefox has told me to get, or recommended and the only two addons i had on firefox was Adblock plus (fanboy subscrip) and Noscript.
Details of what actually happens: go to a youtube link, video loads for about 2 seconds(both video and audio), screen freezes, and flashes maybe once with some small lines across the bottom half of the screen horizontally towards the right corner, then the screen goes blank and makes my laptop dorment, but still running, thus I restart my system.
Sadly now when I system restore there isn't a point far back enough before this problem. So its either i downgrade(which seems to be the only option) or simply stop using firefox, as internet explorer works perfectly fine. however running firefox with no scrip and adblock plus is the ideal browser customisation, which is why this is rather annoying.
so number 1 was the tinyurl theory and i must admit i was abit foolish to follow such a random link, but whats happened has happened.
2: basically there is a major disfunction with the latest firefox that has to with the addons i have included onto firefox and this seems to be causing a terrible effect on my system.
in a nutshell: firefox worked perfectly before upgrading to the new firefox and before i followed this link, the rest of my system is completely normal and virus and error free or so it says, Other browsers seem to work also. safe mode does not cure the problem.
Running on a customised Dell laptop, which is pretty midrange-toprange and hasn't been active long, so it has the general HD video card thats included in all Studio 15 Dell laptops.
any help appreciated.
cheers.
== User Agent ==
Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; MDDC; OfficeLiveConnector.1.5; OfficeLivePatch.1.3; Creative AutoUpdate v1.40.02; AskTbMYC-SRS/5.7.1.11118)

Answer 1

I have had a similar problem with my system. I just recently (within a week of this post) built a brand new desktop. I installed Windows 7 64-bit Home and had a clean install, no problems. Using IE downloaded an anti-virus program, and then, because it was the latest version, downloaded and installed Firefox 4.0. As I began to search the internet for other programs to install after about maybe 10-15 minutes my computer crashes. Blank screen (yet monitor was still receiving a signal from computer) and completely frozen (couldn't even change the caps and num lock on keyboard). I thought I perhaps forgot to reboot after an update so I did a manual reboot and it started up fine.
When ever I got on the internet (still using firefox) it would crash after anywhere between 5-15 minutes. Since I've had good experience with FF in the past I thought it must be either the drivers or a hardware problem. So in-between crashes I updated all the drivers. Still had the same problem. Took the computer to a friend who knows more about computers than I do, made sure all the drivers were updated, same problem. We thought that it might be a hardware problem (bad video card, chipset, overheating issues, etc.), but after my friend played around with my computer for a day he found that when he didn't start FF at all it worked fine, even after watching a movie, or going through a playlist on Youtube.
At the time of this posting I'm going to try to uninstall FF 4.0 and download and install FF 3.6.16 which is currently on my laptop and works like a dream. Hopefully that will do the trick, because I love using FF and would hate to have to switch to another browser. Hopefully Mozilla will work out the kinks with FF 4 so I can continue to use it.
I apologize for the lengthy post. Any feedback would be appreciated, but is not necessary. I will try and post back after I try FF 3.16.6.