[tor-bugs] #21784 [Applications/Tor Browser]: Check `toLocaleString()` methods for locale leaks

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#21784: Check `toLocaleString()` methods for locale leaks
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 Reporter:  gk                                   |          Owner:  tbb-
                                                 |  team
     Type:  task                                 |         Status:
                                                 |  needs_information
 Priority:  High                                 |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  ff52-esr, tbb-fingerprinting,        |  Actual Points:
  tbb-7.0-must-alpha                             |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Changes (by arthuredelstein):

 * cc: boklm (added)
 * status:  new => needs_information


Comment:

 I have manually tested toLocaleString on Array with numbers and Dates, and
 TypedArray with large integers. In both cases, I found that setting
 "javascript.use_us_english_locale" to true (as we already do in Tor
 Browser) was necessary and sufficient to hide the system locale.

 In order to test this, we could write a simple xpcshell test, but we need
 to set the environment variable `LANG` before running it. I couldn't find
 anyway to do this in the standard Mozilla testing framework. Nicolas, is
 this something we could do in your tor-browser-bundle-testsuite?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21784#comment:5>
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