Async live stacks are now enabled by default in Nightly and DevEdition!
The handling of <meta viewport> tags in webpages is now enabled in all current releases of Firefox. The staged roll-out done in release 72 is now complete!
Next steps include doing a UI review of this new panel and showing all workers for registrations.
The RDM Fission project is close to being done. The 3 remaining bugs (1579226, 1604726, 1585121) might be completed as early as the end of this month. At that time, we'll be able to turn on the devtools.responsive.browserUI.enabled pref which will have no noticeable effect on RDM. The only difference is how the RDM UI will be embedded into Firefox.
The rest of the Fission project for DevTools (M2) is progressing well. A lot of work still needs to be completed, but by end of H1 2020, all of the most important DevTools panels should be ready for Fission.