Hacker News Reader

Well, Chrome used to do this too until they removed it in 2016. Internet explorer does this. It was more of a default than a 'feature of Firefox'.

Also, in most normal web pages—at least those not using hideously over-complicated scripting—just pressing your "forward" button (Alt+Right, for example) will navigate forward and restore the edits you had in the form.

I didn't even know this "feature" was available on Firefox (despite using it since version 2). Turns out, it is only enabled on Windows:

http://kb.mozillazine.org/Browser.backspace_action

Maybe it was copied from IE to keep "closer to the platform"?

It's definitely not limited to Windows. I am exclusively a MacOS user (for my workstation, at least) and I have had to disable it on any new Firefox install.