Easier copy/paste error message.

web/viewer.css

@@ -330,7 +330,7 @@ canvas {
   color: black;
   padding: 3px;
   margin: 3px;
-  white-space: pre;
+  width: 98%;
 }
 
 .clearBoth {

web/viewer.html

@@ -114,7 +114,7 @@
         </button>
       </div>
       <div class="clearBoth"></div>
-      <div id="errorMoreInfo" hidden='true'></div>
+      <textarea id="errorMoreInfo" hidden='true' readonly="readonly"></textarea>
     </div>
 
     <div id="sidebar">

web/viewer.js

@@ -346,13 +346,14 @@ var PDFView = {
     };
     moreInfoButton.removeAttribute('hidden');
     lessInfoButton.setAttribute('hidden', 'true');
-    errorMoreInfo.innerHTML = 'PDF.JS Build: ' + PDFJS.build + '\n';
+    errorMoreInfo.value = 'PDF.JS Build: ' + PDFJS.build + '\n';
 
     if (moreInfo) {
-      errorMoreInfo.innerHTML += 'Message: ' + moreInfo.message;
+      errorMoreInfo.value += 'Message: ' + moreInfo.message;
       if (moreInfo.stack)
-        errorMoreInfo.innerHTML += '\n' + 'Stack: ' + moreInfo.stack;
+        errorMoreInfo.value += '\n' + 'Stack: ' + moreInfo.stack;
     }
+    errorMoreInfo.rows = errorMoreInfo.value.split('\n').length - 1;
   },
 
   progress: function pdfViewProgress(level) {