added info in the warning message

lib/hooks/content/content-hooks-frames-web.js

@@ -198,7 +198,7 @@
 	let errorDetected;
 	window.requestAnimationFrame = function (callback) {
 		if (!warningRequestAnimationFrameDisplayed) {
-			console.warn("SingleFile is hooking the requestAnimationFrame and cancelAnimationFrame functions to load deferred images."); // eslint-disable-line no-console
+			console.warn("SingleFile is hooking the requestAnimationFrame and cancelAnimationFrame functions to load deferred images in background tabs."); // eslint-disable-line no-console
 			warningRequestAnimationFrameDisplayed = true;
 		}
 		let requestId;