Added workaround for Firefox performance bug

src/contentScript.js

@@ -166,20 +166,30 @@ function restoreScrollability() {
 	*/
 function startConstantVigilance() {
 // 	console.log("startConstantVigilance");
-	var observer = new MutationObserver((mutationsList, observer) => {
+	var observer;
-		window.requestIdleCallback(() => {
+	var starter = function() {
-			for (var mutation of mutationsList) {
-				killSticky(mutation.target);
-			}
-		});
-	});
-
-	console.log("Commencing vigilance for stickies!");
 		observer.observe(document.querySelector("html"), {
 			attributes: true,
 			childList: true,
 			subtree: true
 		});
+	};
+
+	observer = new MutationObserver((mutationsList, observer) => {
+		// Workaround for Firefox performance bug. Firefox does not properly
+		// coalesce mutations into the mutationsList, instead calling the
+		// callback potentially thousands of times. Therefore we must
+		// disconnect the observer, wait for the main thread to become idle,
+		// and then restart it.
+		observer.disconnect();
+		window.requestIdleCallback(() => {
+			killSticky();
+			starter();
+		});
+	});
+
+	console.log("Commencing vigilance for stickies!");
+	starter();
 }
 
 /*++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*/