Right now you can only use the app manager with the Firefox OS Simulator downloaded by the tool itself. Sometimes you need to use your own Gecko build.

In bug 929061, we added support for starting custom runtime from the Simulator addon. This is one way that AM could connect to a custom Gecko build, though it's a bit awkward if you didn't really need the regular Simulator to start with. In bug 970298, this same strategy will be re-added to the 1.4+ simulators. However, we'd need to come up with something new here if we want it to be easy to use a custom Gecko build without requiring you to go through an existing simulator addon.

Are there bugs for things like: * any remaining UI work * enabling profiles

The Simulator configuration screen can do that. To enable it now, flip devtools.webide.enableRuntimeConfiguration. (In reply to J. Ryan Stinnett [:jryans] (use ni?) from comment #2) > Are there bugs for things like: > > * any remaining UI work > * enabling profiles Bug 1156834 and dependencies will enable it by default, after configurations are persisted and a few other things (see bug 1156834 comment 0).

It is now possible to edit a Simulator's configuration in WebIDE, and to point it to a custom B2G Desktop / Simulator build / Gaia profile.