I don't think that's representative of how Firefox works. I used Firefox similarly in 2013 and didn't see those problems; the users supported by my company, mostly on 4GB machines, also didn't see them.
I have a 112 tabs open right now and Firefox has been running for a couple of weeks, which means thousands more have been opened and closed. It's using 4 GB of memory (EDIT: Which is more than usual, but it's fine with me).
Firefox is still a lot better at RAM and CPU usage when hundreds of tabs are present in the browser. This persists when using e10s.
I have an extension that basically unloads a tab (I guess it freezes the state and serializes it to disk) and frees its ram.
It works very well, so well I'd love to use it on my phone too.
I have commented at length why I use so many open tabs. Basically that's my cache-to-do-list. Once I revisit certain tabs enough times they get upgraded to a bookmark. What bookmarks don't do well but tabs do marvelously is preserve the trajectory and context of how I arrived at the page. Very useful to recreate the state when I visit it later.
It only loads the actual tab when you activate it though, so I don't think all the tabs are being stored in memory, just the ones you activate during a session. I probably actually load about 30 or so during a session, with many more being opened, looked at then closed.
Tab Mix Plus FTW!
That indicates really poor buying decisions! I'm curious about why would this happen.