I should have picked this up before, but: _error: function(aError, aDetails) { ... return Promise.reject(reason); }, and many things throw _error(...) which means we are throwing a promise. There's only 1 thing that actually returns the result or _error(), so the fix is: * _error returns an error object. * whoever wants to return a promise rejected with the error does "return Promise.reject(_error(...)) (the end result is that bug 1148273 works on 38 but fails on 39, as the code checking the error type is seeing the promise and not the error.)

Comment on attachment 8584301 [details] [diff] [review] 0008-Bug-XXXXXXX-fix-error-handling-in-FxAccounts.jsm-to-.patch Review of attachment 8584301 [details] [diff] [review]: ----------------------------------------------------------------- This is fine, but could you also patch the new getSignedInUserProfile method that just landed?

Sorry, I was confused. This "bug" was caused by the "part 1" patch in bug 1139743 not being complete. I've rolled the patch here into that bug and carried the r+ from this patch into that one. > This is fine, but could you also patch the new getSignedInUserProfile method > that just landed? Yep, that's done in that patch.