Revert "Use a link, rather than `window.open`, when opening PDF attachments in Firefox (bug 1661259)"
Revert "Use a link, rather than `window.open`, when opening PDF attachments in Firefox (bug 1661259)"

This reverts commit 1e5d4b6a8025477c3b15b3a320b1cc41ccd7c2bc, since it unfortunately doesn't work in all situations.

Please note that I did *successfully* test the patch in a local Firefox build, obviously with an ad blocker installed.
However, I've now tested the *latest* Nightly-build with my default profile, and unfortunately I can still reproduce the bug there!?

timvandermeij/pdf.js,showpad/mozilla-pdf.js,macroplant/pdf.js,nawawi/pdf.js,Shoobx/pdf.js,macroplant/pdf.js,Shoobx/pdf.js,caremerge/pdf.js,mozilla/pdf.js,macroplant/pdf.js,xavier114fch/pdf.js,mozilla/pdf.js,timvandermeij/pdf.js,xavier114fch/pdf.js,Shoobx/pdf.js,mozilla/pdf.js,caremerge/pdf.js,nawawi/pdf.js,showpad/mozilla-pdf.js,Snuffleupagus/pdf.js,showpad/mozilla-pdf.js,timvandermeij/pdf.js,Snuffleupagus/pdf.js,nawawi/pdf.js,Snuffleupagus/pdf.js