diff --git a/firefox_preferences/chrome/userContent.css b/firefox_preferences/chrome/userContent.css
index 34714f91..2e24e6b6 100644
--- a/firefox_preferences/chrome/userContent.css
+++ b/firefox_preferences/chrome/userContent.css
@@ -1,3 +1,8 @@
 :root {
   scrollbar-color: #2c77ac #2c77ac;
 }
+
+#viewerContainer > #viewer .page > .canvasWrapper > canvas {
+    filter: grayscale(100%);
+    filter: invert(100%);
+}