If the bookmarks sidebar is active, EdgeWare does not work, because the action area is on the right side of the bookmarks sidebar and almost impossible to hit.

Reproduction steps:
1. Activate bookmarks toolbar with Ctrl+B
2. Go crazy trying to find the action area

To clarify, I've taken a screenshot:
https://i.imgur.com/EmFMA2X.png

If the action area is on the left edge of the screen, I can hit it with blind eyes.
The point of MileWideBack/EdgeWise/EdgeWare is to navigate without having to divert attention to a tiny back-button or trying to hit the action area - I just drag my mouse to the left border of the screen & click.

Another bug: For some reason, EdgeWare does not work on addons.mozilla.org