Firefox Home is only for Apple iOS devices, as far as I know.

I believe the Coby is an Android device not a Windows device (so you wouldn't have Internet Explorer on it).

What version of Android? The general solution is to clear the "I'm the default" setting of the current default browser under Manage Applications, but the exact path seems to change with each major version of Android.

Not sure why you would mention Internet Explorer when this tablet is using Android 4.0 (ICS) and not a Windows OS.

The Coby website for the MID9742 says it has a Allwinner Cortex™-A8 however that is misleading as this is really a AllWinner A10 which is a cortex A8 ARM CPU to be accurate. The Cortex A8 is based on the ARMv7 architecture. It also has 1GB RAM and cpu is 1 GHz.

So spec wise this tablet may be able to run the mobile Firefox and since the mobile Firefox 14.0.* does not support tablet interface you may be better off using the mobile Firefox 15.0b3 http://www.mozilla.org/en-US/mobile/beta/