Sometimes tweaking the software is the only way out to force it to behave in a certain way. In course of writing a small shell script on my Linux machine, I too felt a need to customize Firefox.
I was trying to get rid of the Session Restore feature which was added in Firefox 3, as it interfered with my attempts to kill the Firefox process & restart it after a pre-specified interval.
I was about to give up on my efforts before I hit the treasure. Typing about:config in the address bar of Firefox browser would return the following warning.
Once you promise to be prudent with your choices, you are allowed to peep inside :-). I located the browser.sessionstore.resume_from_crash preference name & set it to Boolean False by double clicking on it, which disabled the feature.
That took care of my problem but I was amazed by the sheer amount of customization option that was on offer. Practically every feature of Firefox browser can be tweaked to meet your requirements from here. It’s worth having a look @ this customization option that Mozilla Firefox offers.