Hey @kjemmo, my apologies for the late response.
Unfortunately, based on current information, implementing a toolbar API in 2019 doesn’t look likely. You’re right that we had hoped to land it by the end of 2018. We weren’t quite able to get to it.
This year, we have a clear need to prioritize user security and privacy features. We’re anticipating that these will take most of our engineering resources for the next twelve months. If those projects go smoothly and there’s time left over, we’ll try to get to the toolbar API. When we do, the best place to track progress will be following Bug 1215064.