STR:
  - Go to https://mozilla.github.io/pdf.js/web/viewer.html
  - Click on "Open File" and open a pdf

The `Download` button and the `Current view` one just disappear.
I can reproduce this bug with Firefox nightly, Chrome stable and Epiphany on debian.
PDFViewerApplication.pdfViewer.scrollMode = evt.mode;
}
function webViewerSwitchSpreadMode(evt) {
  PDFViewerApplication.pdfViewer.spreadMode = evt.mode;
}
function webViewerDocumentProperties() {
  PDFViewerApplication.pdfDocumentProperties.open();
}
function webViewerFind(evt) {
  PDFViewerApplication.findController.executeCommand("find" + evt.type, {
    query: evt.query,
    phraseSearch: evt.phraseSearch,
    caseSensitive: evt.caseSensitive,
    entireWord: evt.entireWord,
    highlightAll: evt.highlightAll,
    findPrevious: evt.findPrevious,
  });
}
function webViewerFindFromUrlHash(evt) {
  PDFViewerApplication.findController.executeCommand("find", {
    query: evt.query,
    phraseSearch: evt.phraseSearch,
    caseSensitive: false,
    entireWord: false,
    highlightAll: true,
    findPrevious: false,
  });
}
function webViewerUpdateFindMatchesCount({ matchesCount }) {