Check your settings in the Nvidia control panel , go to manage 3D settings and set the power management mode to prefer maximum performance , the adaptive mode is known to crash your pc in adaptive mode with firefox
If it still crashes do a clean install of your Nvidia display drivers.
If it still continues, you can disable gpu to software rendering in the firefox settings and see if that fixes the problem.
Also uninstall flash and reinstall it to the latest version.
Hope this helps.