add firefox extension template

externs/webextension_polyfill/sidebaraction/Static.hx

@@ -0,0 +1,42 @@
+package webextension_polyfill.sidebaraction;
+
+typedef Static = {
+	/**
+		Sets the title of the sidebar action. This shows up in the tooltip.
+	**/
+	function setTitle(details:SetTitleDetailsType):js.lib.Promise<ts.Undefined>;
+	/**
+		Gets the title of the sidebar action.
+	**/
+	function getTitle(details:GetTitleDetailsType):js.lib.Promise<String>;
+	/**
+		Sets the icon for the sidebar action. The icon can be specified either as the path to an image file or as the pixel data
+		from a canvas element, or as dictionary of either one of those. Either the <strong>path</strong> or the <strong>
+		imageData</strong> property must be specified.
+	**/
+	function setIcon(details:SetIconDetailsType):js.lib.Promise<ts.Undefined>;
+	/**
+		Sets the url to the html document to be opened in the sidebar when the user clicks on the sidebar action's icon.
+	**/
+	function setPanel(details:SetPanelDetailsType):js.lib.Promise<ts.Undefined>;
+	/**
+		Gets the url to the html document set as the panel for this sidebar action.
+	**/
+	function getPanel(details:GetPanelDetailsType):js.lib.Promise<String>;
+	/**
+		Opens the extension sidebar in the active window.
+	**/
+	function open():js.lib.Promise<ts.Undefined>;
+	/**
+		Closes the extension sidebar in the active window if the sidebar belongs to the extension.
+	**/
+	function close():js.lib.Promise<ts.Undefined>;
+	/**
+		Toggles the extension sidebar in the active window.
+	**/
+	function toggle():Void;
+	/**
+		Checks whether the sidebar action is open.
+	**/
+	function isOpen(details:IsOpenDetailsType):js.lib.Promise<Bool>;
+};