add firefox extension template

externs/webextension_polyfill/manifest/WebExtensionDictionaryManifest.hx

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+package webextension_polyfill.manifest;
+
+/**
+	Represents a WebExtension dictionary manifest.json file
+**/
+typedef WebExtensionDictionaryManifest = {
+	var dictionaries : haxe.DynamicAccess<String>;
+	var manifest_version : Float;
+	/**
+		The applications property is deprecated, please use 'browser_specific_settings'
+		Optional.
+	**/
+	@:optional
+	var applications : DeprecatedApplications;
+	/**
+		Optional.
+	**/
+	@:optional
+	var browser_specific_settings : BrowserSpecificSettings;
+	var name : String;
+	/**
+		Optional.
+	**/
+	@:optional
+	var short_name : String;
+	/**
+		Optional.
+	**/
+	@:optional
+	var description : String;
+	/**
+		Optional.
+	**/
+	@:optional
+	var author : String;
+	var version : String;
+	/**
+		Optional.
+	**/
+	@:optional
+	var homepage_url : String;
+	/**
+		Optional.
+	**/
+	@:optional
+	var install_origins : Array<String>;
+	/**
+		Optional.
+	**/
+	@:optional
+	var developer : ManifestBaseDeveloperType;
+	/**
+		In addition to the version field, which is used for update purposes, version_name can be set to a descriptive version
+		string and will be used for display purposes if present. If no version_name is present,
+		the version field will be used for display purposes as well.
+		Optional.
+	**/
+	@:optional
+	var version_name : String;
+};