When installing a Web App from the Firefox Marketplace (or any other place), I cannot launch the app with the default system setup: Gatekeeper blocks the launch because it cannot find a valid certification. This can only be bypassed by disabling Gatekeeper (too much trouble for and unwanted by most users) or launching the application once from the Finder via right-click --> open (which still opens a prompt; many people don't know about this). Chrome Web Apps run just fine without being blocked by Gatekeeper, so there is a way around this issue.

Bug 748977 may provide a way around this issue if it uses a different launch procedure, though that'll certainly be a hack. Bug 746384 seems to be the overall tracking bug while Bug 739636 implemented the webRT installation process for Mac.

What OS X version are you using?

Sorry, 10.9 – should be the same issue on 10.8 with Gatekeeper settings in default mode (i. e. AppStore + signed apps).