about:crashes - An Answer To Why Firefox Crashed.

Did you know that Firefox automatically sends error report to Mozilla whenever your Firefox session crashes?

Related: Downgrading from Firefox 3 to Firefox 2

To find out how many times Firefox have crashed and to know what it is sending to Mozilla, type in about:crashes into the address bar and hit enter. You should see a screen similar to this one:

Click on any crash report to get its details.