[tbb-bugs] #26146 [Applications/Tor Browser]: Setting `general.useragent.override` does not spoof the platform part anymore in ESR 60 which is confusing

[Tor Bug Tracker & Wiki]

#26146: Setting `general.useragent.override` does not spoof the platform part
anymore in ESR 60 which is confusing
-------------------------------------------------+-------------------------
 Reporter:  gk                                   |          Owner:  tbb-
                                                 |  team
     Type:  defect                               |         Status:
                                                 |  needs_information
 Priority:  Medium                               |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  ff60-esr, tbb-fingerprinting-os,     |  Actual Points:
  tbb-8.0-issues                                 |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------
Changes (by mcs):

 * status:  new => needs_information


Comment:

 Replying to [comment:39 tom]:
 > I'm not sure what OSCPU is supposed to be without fingerprinting; but in
 RFP mode, it's the same as User Agent. So if RFP is enabled; you could go
 grab the value from Navigator::GetOscpu and return that instead of
 querying the HTTP header...

 Maybe I am misunderstanding something, but we need the entire, unspoofed
 user agent string. As far as I can tell, the only code that knows how to
 construct such a string is here:
 https://searchfox.org/mozilla-
 central/source/netwerk/protocol/http/nsHttpHandler.cpp#909

 Unfortunately, when `privacy.resistFingerprinting` is true, there is no
 way for code outside of `nsHttpHandler.cpp` to access the string. One
 possible solution would be to add a new attribute to
 `nsIHttpProtocolHandler` such as `unspoofedUserAgent`.

 A question for tom: Is Mozilla likely to switch to this approach and
 accept such a patch?
 A question for gk: Do we want to try this change in Tor Browser?
 Secondarily, should Kathy and I work on a patch this week or someone else
 or should we wait?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26146#comment:42>
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