Comment 1 for bug 342843

I have also experienced this problem, same setup.

The problem does not appear to be limited to firefox for me however, as I have noticed nautilus will also periodically take me to my home folder if left open (as if the alt-home shortcut has been hit.) Another interesting point to note is that my G6 key currently seems to perform this function as well.

I am currently testing g15macro to see if this at least stops the problem (I have removed the key binding from G6.)
Unless I am mistaken I think the G key assignment is also handled by the g15daemon and therefore could be related.