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When searching for contacts in the native Messaging App, nothing happens and no results show. With plenty of contacts manually added too. Simply hitting Enter on the physical keyboard seems non functional and it's the same with the built-in keyboard.
Sorry for the delay responding! This was presumably a problem with Firefox OS, not the Simulator. But since the Messaging app exposes web activities to other apps, this might affect app developers. So it's worth investigating as a Simulator issue. Nevertheless, I can't reproduce this on the latest preview build. Perhaps we fixed it in the last couple months. Therefore I'm closing the issue, but please reopen if you can still reproduce on the latest preview build!
Latest preview build: Windows, Mac, and Linux.