I introduced Bug 165126 while converting a hard-coded sandbox profile into a generated file, and accidentally landed the resulting file in the wrong place. Our test system did not catch this, because none of our tests actually use the plugin sandboxes, so the fact that the "plugin-common.sb" file was in the wrong place was not caught until integration testing. We should create a test plugin (or modify our toy plugin) to use a sandbox profile so that our own tests will catch this kind of error if it happens again.