diff --git a/browser/components/preferences/sync.js b/browser/components/preferences/sync.js
index dcc779d6c6cc..fa1d432625a0 100644
--- a/browser/components/preferences/sync.js
+++ b/browser/components/preferences/sync.js
@@ -439,10 +439,10 @@ var gSyncPane = {
   },
 
   _getEntryPoint() {
-    let params = new URLSearchParams(
-      document.URL.split("#")[0].split("?")[1] || ""
-    );
-    return params.get("entrypoint") || "preferences";
+    let params = URL.fromURI(document.documentURIObject).searchParams;
+    let entryPoint = params.get("entrypoint") || "preferences";
+    entryPoint = entryPoint.replace(/[^-.\w]/g, "");
+    return entryPoint;
   },
 
   openContentInBrowser(url, options) {