Progress is nice, but unfortunately as a user I don't care too much about progress if the bottom line is the same. Sorry to sound disdainful about your efforts, and I know how hard it is, and I have greatest respect for the efforts of Firefox developers, but the bottom line is - it is (was, last time I checked) still leaking like Eratosthenes' sieve, and still becomes unusable after mere days of work. And even admiration for the product and all the history of it can only hold the user for so long when viable alternative is out there.
To counter your anecdote with another, different anecdote with more numbers in it, back in the days of Firefox 4 and subsequent versions, it would not be unusual for my Firefox to hit 500MB to 1GB of RAM usage after a day of browsing. Right now, my Firefox 15 has been running for a day, and about:memory says the total is 363.26MB. Firefox has slimmed down a lot in the past year.