Shockwave flash crashes (a lot) what to do?

I'd start by disabling hardware acceleration.  It's covered in the video troubleshooting guide, here:

Video playback issues

If that doesn't work, you might just take Google Chrome for a spin.  The plugin architecture on Firefox dates back to the late 90's, and it's never really been meaningfully updated.  To address the challenges presented by modern security threats, we retrofitted a sandboxing architecture to Firefox, but the side effect is that there are some intractable stability problems.  Mozilla has expressed some renewed interest in actually collaborating on a next-generation sandbox implementation (unfortunately, without addressing the issue of NPAPI), so hopefully at least some of the more egregious problems will be resolved as part of that effort.

That said, that's pretty forward-looking, so you're going to want something for the interim.

If disabling hardware acceleration *does* make the issues go away, it's time to update your video card drivers.  Once you've done that, re-enable hardware acceleration and see if the problems come back.  If they do, it's a bug in the drivers that hasn't been resolved.  If they're gone, the updated drivers addressed the problem.

Also, if you haven't, you might want to check the disk for errors and do a clean Firefox install as well as Flash Player.