> This last part sounds expensive to do on every startup. Why is it needed? Can our bootstrap script generate and cache it in the install() function? Can we avoid it entirely?

So the plan is to do this once on install/update and cache the results.  We can also have `cfx xpi` do this when the add-on is packaged if the developer goes this route, but the process needs to work without the latter step for development purposes, which means that the developer can still just zip and rename to xpi if they so choose.