Fix missing assignment check mark. Fixes #1271

src/css/popup.css

@@ -538,7 +538,7 @@ span ~ .panel-header-text {
 }
 
 #current-tab > label > input:checked {
-  background-image: url("chrome://global/skin/in-content/check.svg#check-native");
+  background-image: url("/img/check.svg");
   background-position: -1px -1px;
   background-size: var(--icon-size);
 }

src/img/check.svg

@@ -0,0 +1,6 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
+  <path fill="#3c3c3c" d="M6 14a1 1 0 0 1-.707-.293l-3-3a1 1 0 0 1 1.414-1.414l2.157 2.157 6.316-9.023a1 1 0 0 1 1.639 1.146l-7 10a1 1 0 0 1-.732.427A.863.863 0 0 1 6 14z"/>
+</svg>