That’s the wrong way to look at it. Improving the performance of a complex piece of software is not something you do in one fell swoop, or even in a dozen smaller steps. It’s a job of compounding many tiny single–digit percentages over years, and of carefully avoiding performance regressions.
Be as impressed as you want but I think it is a very good sign that developers are taking care of it, and as this is a free to use product we can always be happy if someone boosts performance no matter how much
Very, if only because you'd have said I'm not sure how impressed I should be about saving 4.5 MB these days not all that long ago. Remember when emacs was backronymised to 'eight megabytes and constantly swapping'? That was also not all that long ago. Now 8 megabytes is what some pissant JS library takes as part of some miserable npm package used to bellyflop an ad into your browser window.
"Saving X% of RAM" isn't a thing because RAM is itself a cache of compressed swap space and/or mapped files.
The lesson here is pointer-chasing data structures and trees are a lot more expensive than everyone and most programming languages like to pretend they are.
It's more than that, because generally performance is also much worse if you're using a shit ton of memory. That's because CPUs are bottlenecked by cache. So more memory means cache has to be flushed more often, and there will be more misses, which can greatly impact performance.
But they do keep the active tab of each window in memory. Firefox even continues rendering all active tabs in all windows, even if for windows which are not visible.
Not sure if this 45MB is per browser instance or per tab, but it’s the latter case, 10 windows would save 450MB. >10% on a lower-end device.
I'll happily take performance improvements cause most products lack any efficiency care nowadays.