Canvas data extraction should be allowed when *local* pdf.js is invoked
How to reproduce the issue:
(1) Go to the following URL: https://web.archive.org/web/20180211235741/https://research.torproject.org/techreports/tbb-forensic-analysis-2013-06-28.pdf
(2) Click on the "Toggle Sidebar" button, as in here:
(3) The thumbnails are empty, and in the browser console: Blocked https://web.archive.org/web/20180211235741if_/https://research.torproject.org/techreports/tbb-forensic-analysis-2013-06-28.pdf in page https://web.archive.org/web/20180211235741/https://research.torproject.org/techreports/tbb-forensic-analysis-2013-06-28.pdf from extracting canvas data. re[/pdf.js/web/viewer.js:3311.](/pdf.js/web/viewer.js:3311.`)
Note that it's the local re[/pdf.js/web/viewer.js](/pdf.js/web/viewer.js`) that is invoked and not some bundled pdf.js.