Was it Chrome that came up with tabs? i cant seem to remember if FF had it. If FF didnt have tabs, that is enough for me to say Chrome wiped out the competition.
From Wikipedia (I first saw it using Galeon. I'm probably messing up history here but I think Epiphany was also early with tabs):
The tabbed interface approach was then followed by the Internet Explorer shell NetCaptor in 1997. These were followed by a number of others like IBrowse in 1999, and Opera in 2000 (with the release of version 4 - although a MDI interface was supported before then), MultiViews October 2000, which changed its name into MultiZilla on 1 April 2001 (an extension for the Mozilla Application Suite[8]), Galeon in early 2001, Mozilla 0.9.5 in October 2001, Phoenix 0.1 (now Mozilla Firefox) in October 2002, Konqueror 3.1 in January 2003, and Safari in 2003. With the release of Internet Explorer 7 in 2006, all major web browsers featured a tabbed interface.
Opera was the first browser with any significant market share that supported tabs. I vividly remember switching to Opera somewhere in the 2000s for that very reason.
It also had working bookmark syncing way earlier than the others - that was the second reason for me to use Opera in the 2000-2010 timeframe. I eventually switched to Chrome when it got too good to ignore, and lately to Firefox when it got good enough to compete head-to-head with Chrome.
Opera's technology may not have been tabs, but it allowed the rise of tabbed based browsing. It just used the technology of the time (having it's own windowed interface, which incidentally allowed a tab-like arrangement). It's a bit disingenuous to make the claim that Opera was not instrumental in the development of tabbed based browsing, even if it wasn't specifically using the tab technology earliest.
FF had tabs. IE had already adopted them. Chrome worked a bit better with lots of tabs. Iirc, pre-chrome, a crash (usually flash) in one tab would crash the browser. Chrome fixed that.
Immediately before chrome launched, FF was slowly eating into IE's market share. Chrome was good, but so was FF.
I don't think chrome ever had a lead in FF anything like the lead FF had over IE. Mozilla always had to play with a disadvantage. Still do.