Well luckily for you, and I am sure others, Firefox will allow you to re-enable this in your browser once version 86 rolls out. As cited from the article: Set

Well luckily for you, and I am sure others, Firefox will allow you to re-enable this in your browser once version 86 rolls out. As cited from the article: Set the browser.backspace_action to 0 in the about:config settings panel to re-enable support for the Backspace key as a Back button.