Coincidentally, all of the examples you mention have been a major focus for far more people within Mozilla than their experiments are, and improvements in these areas have really been noticeable if you've been using Firefox lately.
Yes, but these changes take time and they only started working on them when users started leaving for Chrome.
Like many others, I used Firefox for a long time despite it being technically inferior to Chrome, but at some point you say 'fuck it' and make the change.
Mozilla, given their market share, should have been first to offer 64-bit support, separate processes for tabs, sand-boxing and a lot of other stuff, but they've been asleep, because for a long time there was no strong competitor.
Those are accurate comments about Mozilla in the past, but you can't say development currently is bad when they're working exactly on what you say they should be working on (and some other things).
Coincidentally, all of the examples you mention have been a major focus for far more people within Mozilla than their experiments are, and improvements in these areas have really been noticeable if you've been using Firefox lately.