Firefox woes on Ubuntu 7.10

Having switched to Ububtu 7.10, I'm extremely happy with everything about it.

Except for Firefox.

I downloaded general add-ons for browsing, swf playability and.... Shockwave player, I think it was... But those were mainly so Firefox would stop bugging me when pages had flash ads. Anyways...

I notice definite slow-down whilst browsing some sites, most notably, Photobucket. Lines often blur together in it, and it slows my entire computer down to a near-standstill, to the point that the screen goes dark and stops a bit, until I close the tab Photobucket is in, and then everything works great again. I browse and use Photobucket quite a bit, so this is quite an issue for me.
However, I loaded Photobucket via Epiphany browser, and it works perfectly. While it is an alternative, I still like to keep things organized under one window, as Firefox so allows.

And, another irk, no Youtube video's load. The pages around a video work fine, text, ads, the ilk, but the video itself is just shown as a black square, with no play buttons or anything. I tried other sites with similar pages, and no video's load at all. Just that same black square. No plug-in download dialog appears, and everything else is fine, just not the video itself...
I try the same thing in Epiphany, and it's exactly the same, only it makes just the browser malfunction, and I can't close without seeing a 'Not Responding' message pop up.

I'm not a frequent browser of Youtube, but it's an irk to my friends who try to link me video's.

Anyone have any tips to fix this? Am I doing something wrong? I can live with these errors, I just wish more light to be shed as to why they're occuring.

Many thanks in advance.