asynctypes-685526: Sync with changes in Firefox

domtemplate and promise had changed in Firefox. This brings them all
together.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
asynctypes-685526: Report errors to console

It can be hard to work out what has gone wrong with commands so we
log errors to the console.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
Merge branch 'asynctypes-685526' into exec-754315