My guess is the site uses Flash. Do you notice any problems with other Flash media (e.g., games, videos)?

This is some standard guidance that addresses the most common issues with Flash. I'm sure you've seen some of it before, but just in case:

(1) Make sure all recorders/downloaders that interact with Flash media are as up-to-date as possible, or disable them.

(2) Disable hardware graphics acceleration in Firefox and in Flash

(A) In Firefox, un-check the box here and restart:

orange Firefox button (or Tools menu) > Options > Advanced > General > "Use hardware acceleration when available"

(B) In Flash, see this support article from Adobe: http://helpx.adobe.com/flash-player/kb/video-playback-issues.html#main_Solve_video_playback_issues

(3) Disable protected mode (Windows Vista/7/8)

See this support article from Adobe under the heading "Last Resort": Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?

Also, your crash reports might be connected with a known bug. This article describes how to view and copy links to bug reports so you can paste them in a reply here: Troubleshoot Firefox crashes (closing or quitting unexpectedly).

You can also try to update Flash to the latest 11.8 version, your System Details List shows:

1. Shockwave Flash 11.7 r700