I have been assigned to review this document on behalf of the Ops directorate.  In general, I found the document well-written, but the reason I marked it as not ready as I was confused as to its standards track trajectory.  I do not see any kind of inter-operable standard being defined here.  On my reading -- before I noticed it was standards track -- it felt informational.  While it does set out a threat model for the browser, I struggle to see how that needs to be standardized. 

On that threat model note, the abstract indicates that the WebRTC threat model will be laid out, but section 3 defines a more general browser threat model. 

Beyond those items, I noticed various nits and other small items when reading the document.  Most broadly, I feel this document would benefit from a terminology section to define acronyms such as ICE, TURN, STUN, VoIP, etc.  Additionally, in section 3.1, the document refers to "scripts" in a general way.  While the implication is JavaScript code that will run in a browser, I think that kind of context setting might be made more explicit in a terminology section.

Other nits are mentioned below on a section-by-section basis.

Section 1:

s/implementated/implemented/

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Section 3.2:

s/provide a escape hatch/provide an escape hatch/

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Section 4.2:

s/signficant/significant/

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Section 4.2.3:

s/ threats is less severe/threats are less severe/

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Section 4.3:

s/ The calling service is is/The calling service is/

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Section 4.3.2.1:

OLD:

  (a) the browser to trusted UI to provide the name and

I don't grok this sentence fragment.  There seems to be a verb missing, and I'm not sure what your intent is here.

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Section 4.3.2.2:

s/e.g., read aloud over the the voice/e.g., read aloud over the voice/

s/However, it it is well-known/However, it is well-known/