Safari cannot render certain web pages

Safari 5.1.2 cannot render some, but not all, web pages with embedded video and slide shows.

The video window on a page with an embedded video displays a whirling ball and a notation below the video window displays "loading ..." forever. Meanwhile, my router shows no activity.

Web pages with embedded slide shows display the first image in the viewing window. Clicking the forward/back arrows produce no action.

I've reported these problem via Safari's "report a bug" for at least two months but so far there has been no updates.

The most recent Safari aggravation is the discovery that it cannot properly render Apple Support's Express Lane problem reporting web pages. Safari displays the first tab of the site where the product category is selected but stalls on the next tab, which is supposed to display a selection of phrases describing the issue with the product. Instead, the issue description area is blank.

Firefox shares these problems, including stalling on the issue description tab of Express Lane.

Opera works flawlessly.

I have tried emptying Safari's cache and history, even though there is no logical reason why a loaded cache or a large history file should interfere with rendering web pages, as far as I know.

I have also tried resetting Safari. No joy there either.

Has anyone else had this problem and found a solution?