Hold down your Left Shift button, while holding down shift Open Firefox,
You will be represented with this screen
Select Disable All Add-on's
Reset All User Preferences To Firefox Defaults
push enter or click on make changes and restart.
If you want to enable some of your addons again
simply just press Ctrl+Shift+A and select the addons to enable.
If that doesn't fix your issue with crashing most likely it is due to cache
goto options, advanced, network, clear the cache and set a higher limit.
I personally use AddBlocker Plus as the addon to stop spyware/addware/addbots and so forth as it blocks all add's from every site, i would highly recommend this addon to stop this from happening in the future (clicking on an add accidently can cause a lot of issues)