Merge pull request #22799 from nullaus/bug1049790

bug 1049790 - Use one event listener for system time changes. r=fcampo
(cherry picked from commit 408e24a54fb13217428fa9387ca01044a1ea3da4)

Conflicts:
	shared/js/tz_select.js

(cherry picked from commit a2e8bcf542ea41ea8c2acfe847443336c7dea17b)
bug 1049790 - v1.4 specific patch.