Firefox had things (XULRunner, and later running it via Firefox via WebRT). I have no idea about Chrome. Experience learned during the XULRunner era is that M

Firefox had things (XULRunner, and later running it via Firefox via WebRT). I have no idea about Chrome. Experience learned during the XULRunner era is that Mozilla doesn't really want to be a platform, so they don't care very much about API changes. This means that using a shared runtime means apps will randomly break as the runtime is upgraded. Alternatively, you can attempt to keep multiple versions of the runtime around (.Net-style); but since releases are every 6 weeks and downloadable applications don't tend to have that kind of release cadence, you end up with essentially one copy per app anyway. If the platform actually acts like they want to be a platform (the way Qt does, with supported stable releases spanning years as an app gets developed), that might work?