[tor-bugs] #16874 [Tor Browser]: https://sports.yahoo.com/dailyfantasy is broken with Tor Browser 5.0 on Windows

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#16874: https://sports.yahoo.com/dailyfantasy is broken with Tor Browser 5.0 on
Windows
-------------------------+-------------------------------------------------
     Reporter:  gk       |      Owner:  tbb-team
         Type:  defect   |     Status:  new
     Priority:  normal   |  Milestone:
    Component:  Tor      |    Version:
  Browser                |   Keywords:  tbb-usability-website,
   Resolution:           |  tbb-5.0-regression
Actual Points:           |  Parent ID:
       Points:           |
-------------------------+-------------------------------------------------

Comment (by arthuredelstein):

 Browsing to https://sports.yahoo.com/dailyfantasy, I noticed that a
 `window.Intl is undefined` error appears in the JS console on Windows.
 This error is caused by our use of `--without-intl-api` in `.mozconfig-
 mingw` (our Windows build). So I wondered if this error might be causing
 the problem, but our TBB-4.5.3 builds also use `--without-intl-api`.

 I then discovered that a `polyfill.min.js` script is loaded by the page in
 TBB-4.5.3 that compensates for the lack of a built-in `window.Intl`
 object. This file adds `IntlPolyfill` and `Intl` properties to the
 `window` object, such that `Intl === IntlPolyfill` returns true in the JS
 console. On TBB-5.0.2, the page attempts to load `polyfill.min.js`, but
 the server responds with an empty file (200 OK).

 The request headers from the two browser versions are almost identical.
 One difference is the User-Agent, which is controlled by the
 `general.useragent.override` pref:
 * TBB-4.5.3 has `Mozilla/5.0 (Windows NT 6.1; rv:31.0) Gecko/20100101
 Firefox/31.0`
 * TBB-5.0.2 has `Mozilla/5.0 (Windows NT 6.1; rv:38.0) Gecko/20100101
 Firefox/38.0`

 If I set the `general.useragent.override` in TBB-5.0.2 to emptry, or to
 * `Mozilla/5.0 (Windows NT 6.1; rv:38.0) Gecko/20100101 Firefox/31.0` or
 * `Mozilla/5.0 (Windows NT 6.1; rv:31.0) Gecko/20100101 Firefox/38.0`,
 then the Yahoo server returns a non-empty `polyfill.min.js` and the links
 in https://sports.yahoo.com/dailyfantasy are no longer broken.

 So there are two possible solutions to this bug: (1) cross-compile Firefox
 for Windows with the Intl API, and (2) change the User-Agent as above.
 Solution 1 may not be easy (see
 https://bugzilla.mozilla.org/show_bug.cgi?id=1019744#c19), but Solution 2
 seems like an weird thing to do for an issue specific to this one site. On
 the other hand, since we have a habit of disabling dangerous new features,
 there might be an argument for not presenting a User-Agent that claims
 support for 38.0 features.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16874#comment:3>
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