Having problems after PRAM reset

Hi - I reset my PRAM at the suggestion of a Genius bar guy. I've had serious problems ever since. Some of them:
1. Apps won't start. Safari, Drive Genius, iTunes, etc. I get the error message "[App] quit unexpectedly. Click Reopen to open the application again. Click report to see more detailed information and send a report to Apple."

2. Dropbox won't sync anymore

3. Firefox crashes when I use gmail.

4. The Shockwave Flash plugin crashes when I use gmail in Chrome. So does the Google Talk plugin.

5. I can't attach files using gmail in Firefox or Chrome.

There are probably other problems, but I've stopped looking.

Here's what I've done:

Repaired disk permissions (several times) using Disk Utility, once while booted from the SL install disk.

Repaired disk while booted from SL install disk. Verfied after that and got a message that the disk appeared to be ok.

Reinstalled Dropbox

Reinstalled Firefox and Chrome

Disabled one of two Flash plugins that showed up in Chrome

Here's some info on the machine: Mid-2007 Intel iMac, 2GHz Core 2 Duo, 3GB RAM, Running OS 10.6.8

I have a Time Machine backup, but I wonder if it would help. My understanding is that PRAM and VRAM live in the firmware, so Time Machine wouldn't affect it. I'd love to be wrong about that, but I'm nervous about trying other stuff at this point.

Any help? I'd rather not do anything drastic like reinstall the OS.

Thanks for any advice.