That said, even with the 9 add-ons I'm using, I was hoping I could see a total memory usage on startup to be closer to 225MB.
All browsers do have memory leaks but the fact that FF's memory continually increases to the point where I have to restart the whole browser every day is mentally tiring. This is where Chrome just got it right.
That’s really not the case any more.
What was happening was that extensions had references to dom-nodes of a page, that prevented the page from being unloaded when you close the tab. Unless of course, the extendion author bothered to fix this from their side. Now, an extension has essentially "weak references" to dom nodes. (think: symlink)
So far in my testing and browsing, it is.
This is also a useful way to start looking at a suspected leak: visit a page and hit about:memory to see what it's using, then close the tab and check about:memory again to see whether it's freeing everything.