I use virtual machines fairly frequently with older versions of Firefox installed in them. It’s almost shocking how much better and more capable those supposedly out-of-date browsers are than any modern version of FF.
During the recent era of observing Firefox’s crapification, it’s been strange watching otherwise-smart people perfectly parrot the contention that it was just impossible to have Firefox be both configurable and secure — that it was in fact so difficult and out-of-bounds to even ask for that it should not even be considered.
Of course, the reality is that continuing to allow the browser to be customized was no harder than making Firefox secure, or rather “secure,” and in some ways continuing to allow customization would’ve made the project and product more popular, thus garnering more users, allowing it to flourish, and thus allowing more initiatives of all sorts.
I think the story of the last twenty years of my life has been realizing that “smart” people are far less so than given credit for, and these days I continually revise downward my estimate of their capabilities. The events with Firefox are just another example and reason that has occurred.