Deliberately inefficient software like slow FireFox (gecko Seamonkey)

In 2010 FIrefox / Seamonkey 2.0 took 90MB of RAM and 2 seconds to render a page. In 2015 Firefox / Seamonkey 2.33 takes 300MB of RAM and 4 seconds to render the same page.

The increase in functionality in those 5 years is little enough that I don't notice any change as far as features. If I run the 2010 browser today some text and other objects on a page will often be incorrectly positioned but that is minor, and of course the javascript will fail and if the site requires javascript then the site is not usable.

They do this on purpose as part of a deal to make people buy faster computers. This free / open source software is crap. I would pay $10 for a real browser. WebKit / Blink browsers are a bit faster but the memory use is even worse.

What is the solution to this problem?

If you wish to experiment with Seamonkey and you have the new version installed then be sure to make another Seamonkey user profile when starting the older version. Even with doing that I think it removes all of your addons.