Firefox has historically been a memory hog, but Mozilla has been aware 
of the issue and has been working hard to minimize the problem.  This 
website which documents the results of these efforts may be useful to 
you, though it is really intended for techies (at least people "techier" 
than me):  https://areweslimyet.com/

The FAQ is helpful, and here is a quotation from that FAQ to whet your 
appetite:

"What is this site?

Are We Slim Yet? is a Firefox memory benchmark and a site for 
visualizing the historic results of that benchmark.

Are we Slim Yet? was created by John Schoenick of Mozilla's MemShrink 
team. The MemShrink team was formed in June 2011, and is tasked with 
monitoring and reducing Firefox's memory usage.

This site allows us to observe long-term trends in memory usage and 
hopefully catch regressions before we ship them to users.

Come say hi on GitHub."

Best,

Tom.

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