"Component is not available" nsresult: "0x80040111 (NS_ERROR_NOT_AVAILABLE)"

[javanoclaw]

I found some compatibility issues in Firefox browser.

Environment
Browser: Firefox 60.7.0esr (64 bit)
Browser download link: ftp.mozilla.org/pub/firefox/releases/60.7.0esr/

I try use these codes to fix this issues:

var _getComputedStyle = getComputedStyle(target, '::-webkit-scrollbar');
var width = '0px';
var height = '0px';
try {
    width = _getComputedStyle.width,
    height = _getComputedStyle.height;
}catch(e) {
    width = '0px';
    height = '0px';
}

Can these codes be merged into the master branch?

[defaultjacky]

getComputedStyle(document.body, '::-webkit-scrollbar');

1. 这个伪类 ::-webkit-scrollbar 在 Firefox 上不支持（非标）
2. 在 Firefox 62 之前，视窗上未展示的元素（Window with no presentation） getComputedStyle 返回的是 null

所以出现这种声明了要匹配的伪元素的字符串反而被浏览器识别为元素不存在，返回了 null
https://bugzilla.mozilla.org/show_bug.cgi?id=1467722
https://bugzilla.mozilla.org/show_bug.cgi?id=1471231