[eejdoowad]

An extension overlay API would have saved me so much pain when building Saka (saka.io). There are two options for injecting UI today:

1. Inject UI directly into the document

2. Inject an iframe containing the UI into the document

Both rely on manipulating the document, which can be used to fingerprint users. Most developers opt for 1 because it requires no setup and lets the content script synchronously access the UI. 2 is needed when the injected UI containing sensitive information.

I'd like an extension overlay API that lets you inject: 1. UI local to the tab 2. UI that persists across all tabs

In a brief #webextensions IRC discussion, I was told an overlay API isn't viable for a number of reasons, one of which is multiple extensions may conflict.

[hawski]

Did they tell you how the extensions may conflict? I don't understand what it means. Couldn't it work like e.g. context menu does already for extension icon?

[eejdoowad]

What happens when two extensions try to place a widget in the same location? Chaos. Not that the status quo is any better.

Interestingly, Firefox's sidebar API only allows a single sidebar to be shown.

[drdaeman]

I still don't get it. What problem they're trying to avoid?

It's exactly the same if two extensions would currently try to manipulate the page by adding a frame (or, worse, a <div> with non-isolated UI) to the same location.

The only difference is, with out-of-page widgets (e.g. overlay regions or popouts), they won't be visible in the page's DOM.

[eejdoowad]

My understanding is that if they do implement an API, they want it to be better than the status quo, not the same.