--- a/browser/themes/shared/controlcenter/panel.inc.css
+++ b/browser/themes/shared/controlcenter/panel.inc.css
@@ -6,16 +6,22 @@
 %filter substitution
 %define identityPopupExpanderWidth 38px
 
 /* Hide all conditional elements by default. */
 :-moz-any([when-connection],[when-mixedcontent],[when-ciphers],[when-loginforms]) {
   display: none;
 }
 
+/* This is used by screenshots tests to hide intermittently different
+ * identity popup shadows (see bug 1425253). */
+#identity-popup.no-shadow {
+  -moz-window-shadow: none;
+}
+
 /* Show the right elements for the right connection states. */
 #identity-popup[connection=not-secure] [when-connection~=not-secure],
 #identity-popup[connection=secure-cert-user-overridden] [when-connection~=secure-cert-user-overridden],
 #identity-popup[connection=secure-ev] [when-connection~=secure-ev],
 #identity-popup[connection=secure] [when-connection~=secure],
 #identity-popup[connection=chrome] [when-connection~=chrome],
 #identity-popup[connection=file] [when-connection~=file],
 #identity-popup[connection=extension] [when-connection~=extension],

--- a/browser/tools/mozscreenshots/mozscreenshots/extension/configurations/ControlCenter.jsm
+++ b/browser/tools/mozscreenshots/mozscreenshots/extension/configurations/ControlCenter.jsm
@@ -257,17 +257,17 @@ async function loadPage(url) {
 
 async function openIdentityPopup(expand) {
   let browserWindow = Services.wm.getMostRecentWindow("navigator:browser");
   let gBrowser = browserWindow.gBrowser;
   let { gIdentityHandler } = gBrowser.ownerGlobal;
   gIdentityHandler._identityPopup.hidePopup();
   // Disable the popup shadow on OSX until we have figured out bug 1425253.
   if (AppConstants.platform == "macosx") {
-    gIdentityHandler._identityPopup.style["-moz-window-shadow"] = "none";
+    gIdentityHandler._identityPopup.classList.add("no-shadow");
   }
   gIdentityHandler._identityBox.querySelector("#identity-icon").click();
   if (expand) {
     // give some time for opening to avoid weird style issues
     await new Promise((c) => setTimeout(c, 500));
     gIdentityHandler._identityPopup.querySelector("#identity-popup-security-expander").click();
   }
 }