diff --git a/browser/extensions/mortar/host/common/ppapi-runtime.jsm b/browser/extensions/mortar/host/common/ppapi-runtime.jsm
index c97851663df8..349dee9883b8 100644
--- a/browser/extensions/mortar/host/common/ppapi-runtime.jsm
+++ b/browser/extensions/mortar/host/common/ppapi-runtime.jsm
@@ -1720,6 +1720,7 @@ class PPAPIInstance {
       let mouseEventInit = {
         altkey: event.altkey,
         button: event.button,
+        buttons: event.buttons,
         clientX: event.clientX - rect.left,
         clientY: event.clientY - rect.top,
         ctrlKey: event.ctrlKey,
@@ -1820,6 +1821,12 @@ class PPAPIInstance {
         // We need permission for showing print dialog to get print settings
         this.mm.sendAsyncMessage("ppapipdf.js:getPrintSettings");
         break;
+      case 'openLink':
+        this.mm.sendAsyncMessage("ppapipdf.js:openLink", {
+          url: message.url,
+          disposition: message.disposition
+        });
+        break;
       case 'viewport':
       case 'rotateClockwise':
       case 'rotateCounterclockwise':
@@ -3126,25 +3133,37 @@ dump(`callFromJSON: < ${JSON.stringify(call)}\n`);
 
       if (event instanceof KeyboardInputEvent) {
         if (event.domEvent.location == event.domEvent.DOM_KEY_LOCATION_NUMPAD) {
-          modifiers &= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_ISKEYPAD;
+          modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_ISKEYPAD;
         } else if (event.domEvent.location & event.domEvent.DOM_KEY_LOCATION_LEFT) {
-          modifiers &= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_ISLEFT;
+          modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_ISLEFT;
         } else if (event.domEvent.location & event.domEvent.DOM_KEY_LOCATION_RIGHT) {
-          modifiers &= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_ISRIGHT;
+          modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_ISRIGHT;
         }
 
         if (event.domEvent.repeat) {
-          modifiers &= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_ISAUTOREPEAT;
+          modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_ISAUTOREPEAT;
         }
       } else if (event instanceof MouseInputEvent) {
-        if (event.domEvent.buttons && 0x01) {
-          modifiers &= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_LEFTBUTTONDOWN;
+        if (event.domEvent.buttons & 0x01) {
+          modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_LEFTBUTTONDOWN;
         }
-        if (event.domEvent.buttons && 0x04) {
-          modifiers &= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_MIDDLEBUTTONDOWN;
+        if (event.domEvent.buttons & 0x04) {
+          modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_MIDDLEBUTTONDOWN;
         }
-        if (event.domEvent.buttons && 0x02) {
-          modifiers &= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_RIGHTBUTTONDOWN;
+        if (event.domEvent.buttons & 0x02) {
+          modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_RIGHTBUTTONDOWN;
+        }
+        if (event.domEvent.type == 'mouseup') {
+          // mouseup event indicates the key released only in domEvent.button
+          // rather than domEvent.buttons, but PDFium do use modifiers to
+          // determine which button is released. So we make it up here.
+          if (event.domEvent.button == 0) {
+            modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_LEFTBUTTONDOWN;
+          } else if (event.domEvent.button == 1) {
+            modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_MIDDLEBUTTONDOWN;
+          } else if (event.domEvent.button == 2) {
+            modifiers |= PP_InputEvent_Modifier.PP_INPUTEVENT_MODIFIER_RIGHTBUTTONDOWN;
+          }
         }
       }
 
diff --git a/browser/extensions/mortar/host/pdf/chrome/js/viewport.js b/browser/extensions/mortar/host/pdf/chrome/js/viewport.js
index b2ea4538ae56..389978318b55 100644
--- a/browser/extensions/mortar/host/pdf/chrome/js/viewport.js
+++ b/browser/extensions/mortar/host/pdf/chrome/js/viewport.js
@@ -782,6 +782,13 @@ class Viewport {
       case 'goToPage':
         this.page = message.page;
         break;
+      case 'navigate':
+        this._doAction({
+          type: 'openLink',
+          url: message.url,
+          disposition: message.disposition
+        });
+        break;
     }
   }
 }
diff --git a/browser/extensions/mortar/host/pdf/ppapi-content-sandbox.js b/browser/extensions/mortar/host/pdf/ppapi-content-sandbox.js
index 02232284c49c..4c3c1eeaadd2 100644
--- a/browser/extensions/mortar/host/pdf/ppapi-content-sandbox.js
+++ b/browser/extensions/mortar/host/pdf/ppapi-content-sandbox.js
@@ -180,6 +180,31 @@ mm.addMessageListener("ppapipdf.js:printPDF", ({ data }) => {
   });
 });
 
+mm.addMessageListener("ppapipdf.js:openLink", ({data}) => {
+  const PDFIUM_WINDOW_OPEN_DISPOSITION = {
+    CURRENT_TAB: 1,
+    NEW_FOREGROUND_TAB: 3,
+    NEW_BACKGROUND_TAB: 4,
+    NEW_WINDOW: 6,
+  };
+  switch(data.disposition) {
+    case PDFIUM_WINDOW_OPEN_DISPOSITION.CURRENT_TAB:
+      containerWindow.location.href = data.url;
+      break;
+    // We don't support opening in background tab for now. Just open it in
+    // foreground tab.
+    case PDFIUM_WINDOW_OPEN_DISPOSITION.NEW_FOREGROUND_TAB:
+    case PDFIUM_WINDOW_OPEN_DISPOSITION.NEW_BACKGROUND_TAB:
+      containerWindow.open(data.url);
+      break;
+    case PDFIUM_WINDOW_OPEN_DISPOSITION.NEW_WINDOW:
+      containerWindow.open(data.url, "",
+        "noopener=1,menubar=1,toolbar=1," +
+        "location=1,personalbar=1,status=1,resizable");
+      break;
+  }
+});
+
 mm.addMessageListener("ppapipdf.js:save", () => {
   let url = containerWindow.document.location;
   let filename = "document.pdf";