For mozilla#11838: trigger fallback bar after user clicks in pdf

Author: emalysz

web/app.js

@@ -189,6 +189,8 @@ const PDFViewerApplication = {
   externalServices: DefaultExternalServices,
   _boundEvents: {},
   contentDispositionFilename: null,
+  _hasInteracted: false,
+  _isAcroFormPresent: false,
 
   // Called once when the document is loaded.
   async initialize(appConfig) {
@@ -868,10 +870,16 @@ const PDFViewerApplication = {
       PDFJSDev.test("MOZCENTRAL || GENERIC")
     ) {
       // Only trigger the fallback once so we don't spam the user with messages
-      // for one PDF.
+      // for one PDF. For forms, it should only be triggered once the user has
+      // clicked within the PDF.
       if (this.fellback) {
         return;
       }
+
+      if (featureId === UNSUPPORTED_FEATURES.forms && !this._hasInteracted) {
+        return;
+      }
+
       this.fellback = true;
       this.externalServices.fallback(
         {
@@ -1317,7 +1325,7 @@ const PDFViewerApplication = {
 
     if (info.IsAcroFormPresent) {
       console.warn("Warning: AcroForm/XFA is not supported");
-      this.fallback(UNSUPPORTED_FEATURES.forms);
+      this._isAcroFormPresent = true;
     }
 
     if (
@@ -2473,6 +2481,11 @@ function webViewerWheel(evt) {
 }
 
 function webViewerClick(evt) {
+  PDFViewerApplication._hasInteracted = true;
+  if (PDFViewerApplication._isAcroFormPresent) {
+    PDFViewerApplication.fallback(UNSUPPORTED_FEATURES.forms);
+  }
+
   if (!PDFViewerApplication.secondaryToolbar.isOpen) {
     return;
   }