Remove the `hasPrefixedFirefox` functionality from the `external/builder/builder.js` file
Remove the `hasPrefixedFirefox` functionality from the `external/builder/builder.js` file

This functionality has been completely unused ever since PR 9566 (two years ago).

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