Phillip Corcoran :
It manages memory better than Chrome (and uses less of it with multiple tabs).
Less prone to crashing while using plugins.
That's actually the reason I switched from Firefox to Chrome. If a plugin crashed in Firefox, it froze every Firefox tab I had open. I had to kill the entire program (losing all my tabs). Chrome forked a new instance of itself for every tab (which is why it eats so much more memory). So if a plugin crashed, it only froze the one tab. (Dunno if Firefox has addressed this in recent years.)
However, Chrome has a long-standing bug where it doesn't release all the memory from closed tabs. So its memory footprint will slowly grow over time. I use Gmail in Chrome on a virtual machine, and that's pretty much the only thing that Chrome browser does. When I first start it, it only takes about 300 MB. But if I check its memory use after about a month, it's up around 2 GB with multiple instances in the process list that seem to be leftover remnants from closed tabs. It's pretty simple to exit and restart Chrome to free up that memory though.