See How to fix preferences that won't save for possible causes and solutions.

You can disable the crash reporter via the file application.ini in the Firefox program folder.

[Crash Reporter]
Enabled=0

• Ahem* but... where can I find that 'ini' file in the Firefox program folder?

C:\Program Files\Mozilla Firefox\application.ini

Be aware that making changes to files in the Firefox program folder is not recommended and that you most likely need to repeat the edits after each update. Also such changes can cause the updater to download and apply a full update instead of a small incremental update.

Good point on incremental updates I added a Environmental User Variable instead, as per info listed here:

http://kb.mozillazine.org/Breakpad

and here:

https://developer.mozilla.org/en/Environment_variables_affecting_crash_reporting

But does that disable the plugin crash reporter too? Or only the crash reporter for when the entire app crashes? Because what I'm reading the one in Options>Advanced is for plugin crashes.