Revert "Drop support for Gecko 23 or olders"

This reverts commit 9ef9ea36761278a998ea76f8f4b1fac7fe4c1b66.
Revert "Migrate to Promise.jsm"

This reverts commit f3df14f4304e57b213bc0cb977b8cc7213045630.
Wait until the initial window is completely started