Provide a proper setting to disable the new navigation toolbar on mobile

[caylin]

The entire reason many of us switched away from other browsers on mobile was to escape this kind of awful UI. Nobody wants this:

https://connect.mozilla.org/t5/discussions/firefox-mobile-toolbar-redesign-needs-a-compact-mode/m-p/...

https://www.reddit.com/r/firefox/comments/1e252ov/the_new_navbar_design_on_android_nightly_is/ 

[Jon]

Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.

[cannoness]

Seconded. Don't just pop things up like this on users, allow them to opt in.

Covers the bottom of "fixed" pages that scrolling isn't enabled on. We pull to refresh and swipe to go back anyway, we did not need ui for this.

[stefano]

I don't like the new UI at all: I have a samsung s23 and its screen is 6.1 inches, so not too big and I'd like to have more space for the web pages, not less.