This is a feature request. Phones are getting bigger while my hand isn't. For one-handed use, my thumb can only reliably cover a portion of the bottom right of the screen. I'd like an option to be able to move the URL bar to the bottom for easier one-handed use when my other hand is holding something else.
CC'ing Aaron and Ian to take a look on this.
We've explored this as an option in the past, but I don't think we have any near term plans to make this into a thing. Unfortunately the way our UI works, it's not as simple as just repositioning the title bar and being done with it -- it would also involve a pretty major rework of how the tabs tray interacts with this new positioning, how about:home works, how the Reader mode toolbar works, etc. I never like to wontfix ideas I think are interesting, but I don't see this happening any time soon unfortunately.