I've been using Firefox as my daily browser at work, home, and on my mobile devices, and I've literally never had issues with Firefox taking up too much RAM. Chrome on the other hand was always one of the main culprits when my computer(s) would start to slow down.

This is the problem with anecdotal evidence; everybody's subjective experiences are slightly different and further colored with their own biases, so you can never get hard facts out of it.