Binding on role attribute not working in Firefox

**I'm submitting a bug report**

* **Library Version:**
2.3.1

* **OS**
Kubuntu 18.04

* **Browser:**
Does not work in Firefox 67.0
Does work in Chromium 74.0.3729.169

**Current behavior:**
Binding on the role attribute of an element does not work correctly. The role attribute is completely omitted, either using `role.bind` or the `role` attribute with interpolation.

**Expected/desired behavior:**

Unfortunately, the Gist Run is not saving at the moment, so I will just show some sample code:

* app.html
```

Toggle presentation role


Presentation: ${presentation}


Hello
world!

```
* app.js
```
export class App {
presentation = true;
}
```

* **What is the expected behavior?**
The role attribute is shown and updated when the binding changes.

* **What is the motivation / use case for changing the behavior?**
I want to use the role attribute for accessibility purposes.

Possibly related to #486.

Start by reproducing the sample in app.html with the App class from app.js in Firefox and compare the role attribute behavior with Chromium. Read the context of related issue #486 and trace the binding behavior for role; done means the role attribute is present and updates when presentation changes.

Written by the indexing model from the issue text.