It couldn't have taken you years. Firefox 4 was only released in March of this year. Firefox 5 came three months later in June. Firefox 6 was two months later in August, and Firefox 7 now comes a little over a month afterwards.
I'm a great believer in that. However, bugs have been fixed, memory leaks plugged, rendering times improved. Personally the promise of more effcicient memory use has me chomping at the bit - FF runs like molasses on my 768MB Athlon 1.1GHz.
Sure it could. Firefox 3.0 was released in June 2008, 3.5 in June 2009 and 3.6 January 2010. If he just upgraded then he could have been on Firefox 3.x for over 3 years.