I managed to solve this problem myself! It turns-out that I had somehow unchecked "Remember visited pages . . ." in Firefox>Tools>Options>History, and when I rechecked it, all the pages I now visit via Google have begun to change their title colors once again when I return to the search page.
Thanks to anybody who might have taken the time and courtesy to try and help me!
Thanks, too, to "Intelliot" for welcoming me to the Google Community with a PM! I tried to thank him with a Private Message of my own, but your system says that
I must have a minimum of 15 posts before I can even
send a PM of my own (this is the first forum that I've ever been that has such a strange

rule)!