You might need to check if the cooler is properly mounted on the cpu, if it's not firmly and exactly mounted on top then it won't cool good enough.

^ & ^^ Tnx. 
So Intel was using some kind of substandard heat transfer compound between the CPU & lid?
Did they stop doing that yet?

Okay, my CPU is an AMD Athlon 64 X2 dual core processor 4400+, and not Intel, which came to me 6 or 8 years ago as a custom build with an aftermarket CPU cooling fin & fan unit.
I did watch the 'delidding' video, and don't think I want to try that, and anyway mine is an AMD.

Sometime last year, the ASUS mobo told me the CPU fan died and was refusing to boot.
So I had to pull the CPU cooling fin unit anyway to replace the custom CPU fan with a factory-issue ASUS CPU fan that came with the mobo and which I had kept in storage.
In doing so, I had to replace the silver paste.
I had a tube of some 'arctic silver' (I think that is the name) unopened 'in case of need', and I carefully cleaned off the CPU and mating surface of the cooling fin unit, and reapplied fresh silver paste.
So the only thing I can think of is if I somehow did it wrong, but I had watched a video on how to do it first and tried to copy the vid's instructions carefully.
But the crashes only started happening a few months ago, and seem to be related to Adobe updates and online videos, altho I'm only guessing.

The original video card was an NVidia 6800, which quit last year, and was replaced with an NVidia GTS 450, in case that might be a factor.

Go here and make sure it can and is using the HTML5 player, instead of using the default flash based player: https://www.youtube.com/html5

^Got it, & tnx. 
PaleMoon & Seamonkey seemed the most crashy before.
IE, PaleMoon, & Seamonkey had to be switched; FF & Chrome were already set to it.
The TOR Vidalia FF is really 'iffy' about playing any vids at all, but was already set to it.

Do you think DC's ProcessTamer would help, or is only going to add more overload to the OS?
I have tried both with and without using it, and can't decide which way is better.

MY pc crashed with a BSOD tonight during an action scene while playing a movie on a DVD with VLC media player.
Sounds like some of you guys really think I should pull my CPU cooling fan & fins and give them a fresh cleaning & silvering, so I'm thinking about it.
I've been feeling kind of like the flu lately; it's not, it's just fatigue, but I'm not at my most focused, so I may not get to it right away.
I seem to remember a yt vid suggesting the use of coffee filters for a lint-free cleaning rag substitute.
Or I could use a bunch of q-tips.
I could also use naptha (lighter fluid) instead of 70% rubbing alcohol.

My PaleMoon also uses the Self-Destructing Cookies add-on, preventing permanent yt settings.

That would explain why it keeps reverting to default of flash. The setting is stored in a cookie, per browser, rather than in your account to work across all browsers.

^ If you need urgent help, you migth want to make that a new thread instead of burying it in this one.  Just my thoughts...