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### Description

Please provide a detailed description of the bug, how to reproduce it, and the
expected behavior.  Always include a code snippet, screenshot, any errors
reported in the console, and the model to help us understand and fix the
problem.

#### Live Demo
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https://glitch.com/edit/#!/model-viewer
<!-- ...or provide your own repro URL -->

### Version
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- model-viewer: vX.X.X

### Browser Affected
<!-- Check all that apply and please include the version tested (try chrome://version) -->
- [ ] Chrome, version: xx.x.xxxx.xx
- [ ] Edge
- [ ] Firefox
- [ ] IE
- [ ] Safari

### OS
<!-- Check all that apply and please include the version tested -->
- [ ] Android
- [ ] iOS
- [ ] Linux
- [ ] MacOS
- [ ] Windows

### AR
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If your issue involves AR, please check which AR modes reproduce it. If you're
not sure, restrict to one at a time using the `ar-modes` attribute. We can only
control WebXR mode in this project, but we will forward SceneViewer bugs to the
appropriate team.
 -->
- [ ] WebXR
- [ ] SceneViewer
- [ ] QuickLook