add firefox extension template

externs/webextension_polyfill/find/RectsAndTexts.hx

@@ -0,0 +1,13 @@
+package webextension_polyfill.find;
+
+typedef RectsAndTexts = {
+	/**
+		Rectangles relative to the top-left of the viewport.
+	**/
+	var rectList : Array<Rectangle>;
+	/**
+		an array of strings, corresponding to the rectList array. The entry at textList[i]
+		contains the part of the match bounded by the rectangle at rectList[i].
+	**/
+	var textList : Array<String>;
+};