Bug 963216 - Uplift Add-on SDK
Bug 949213 - Strings for content onboarding screen r=mbrubeck

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extra : rebase_source : 83ec63f05ec73be87fdc161833ac4f88c8c9bfcb
Bug 960144 - Toast notification image implementation r=msamuel

--HG--
extra : rebase_source : e412fda60c6a0ab964e62a209e1a732eb8e74b5e
Bug 963885 - Disable mozdevice tests in make check until we can address they way they cause builds to be RETRYed
Merge m-c to f-t
Bug 957460 - Add Firefox Accounts widget for customization panel r=gijs
Bug 962709 - Fix about:home's sync entry point to work with about FxAccounts
Bug 957436 - Show doorhanger for first fxa-based sync