Provide a uuid function fallback which doesn't fail in the Tor Browser.

src/lib/uuid.js

@@ -1,6 +1,15 @@
 'use strict';
+
 function uuid() {
-  return ([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,
-    c => (c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4)
-          .toString(16));
+  try {
+    return ([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,
+      c => (c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4)
+            .toString(16));
+  } catch (e) {
+    // fallback, as the Tor Browser seems to fail above
+    uuid = () => 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
+      let r = Math.random() * 16 | 0, v = c == 'x' ? r : (r & 0x3 | 0x8);
+      return v.toString(16);
+    });
+  }
 }