如何将复制功能添加到Firefox插件

Question

我设计了一个firefox插件，该插件具有一个附加到javascript文件的manifest.json。这会在选择文本并单击鼠标右键时启动搜索。我需要复制已选择的文本。

console.log("hello hi")

function getSelectionText() {
    var text = "";
    if (window.getSelection) {
        text = window.getSelection().toString();
    } else if (document.selection && document.selection.type != "Control") {
        text = document.selection.createRange().text;
    }
    return text;
}




function handleRightClick(click_event) {

    if (getSelectionText() !== "") {
		console.log(JSON.stringify(click_event, null, 4))
		click_event.preventDefault()

	    console.log("selection text: "+getSelectionText())
		
		var base_url1 = "https://www.google.com/search?safe=off&hl=en&source=hp&ei=s0b9W4PmIIaCyAOZwrawAw&q="+getSelectionText().replace(" ","+")
   
		window.open(base_url1, 'ab');
			
    }
}

document.addEventListener('contextmenu', event => handleRightClick(event));

现在如何实现此>> document.execCommand（“ copy”）; 我在Firefox中收到失败的错误