Intent to ship: -less RDM

Hi all, Later this week, we’ll be enabling a new version of the Responsive Design Mode tool that no longer relies on as part of the initiative to make DevTools Fission-compatible. For now, the pref will only be enabled in Firefox Nightly as we work with QA to ensure the stability of the tool.

Re: Intent to ship: -less RDM

Thanks Micah, and everybody else who's been working on this! As someone who's had to struggle at times with the special tunneling and frameloader swapping that we do for the moziframe stuff for RDM, this is a very very welcome change, and will allow us to get rid of some pretty confusing front-end