When running on Firefox 73.0b8 on Linux, I encounter a "NotSupportedError" at @polymer/polymer/lib/mixins/element-mixin.js version 3.3.1 in `_attachDom.` The line in question reads:

`n.attachShadow({mode: 'open', shadyUpgradeFragment: dom});`

The error occurs because `n` is a `FORM` element which has no shadow DOM. Chrome 79.0.3945.130 executes this without problem.

Setting a breakpoint at this line reveals a difference between the two browsers in how this function is called:

Firefox:
1. n = A `FORM` element
No further calls

Chromium:

1. n = paper-button
2. n = paper-button
3. n = iron-ally-announcer
4. n = iron-ally-announcer
5. n = paper-input
6. n = paper-input
7. n = ... (I cannot decipher what the object is)
8. n = ... (I cannot decipher what the object is)
9. n = iron-input
10. n = iron-input

The HTML being executed is as follows:
```

configurator- Log in



import('@polymer/iron-form/iron-form.js');
import('@polymer/paper-input/paper-input.js');
import('@polymer/paper-button/paper-button.js');

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function submitForm(e) {
document.getElementById("_form").submit();
}



Configurator version . ©2018

```