Merge pull request #15815 from davidflanagan/bug956811

Bug 956811: ugly workaround that abuses the settings db for interapp communication r=jporter(cherry picked from commit 2c64a463f6bb053a05326ee1b6c5236eb31b898c)
Merge pull request #15873 from davidflanagan/bug956811-v1.3

Merge pull request #15815 from davidflanagan/bug956811