To enable remote xul apps stringbundles should be usable via http. Perhaps a new attribute could be added to strinbundle, eg delayed, which controls whether the resource will be loaded synchronously or asynchronously.
This bug is related to bug #26291 , which is about loading stringbundle async for perf reasons. IMHO, the API should provide both methods and the XUL tag should default to sync. I guess loading synchronized is 99% ok for local XUL, but perhaps a problem for remote XUL.
setting status to New.