_ff-addon-snippet-SSS - using style sheet service

_ff-addon-snippet-SSS.js

var sss = Components.classes['@mozilla.org/content/style-sheet-service;1'].getService(Components.interfaces.nsIStyleSheetService);
var ios = Components.classes['@mozilla.org/network/io-service;1'].getService(Components.interfaces.nsIIOService);
try {
sss.unregisterSheet(cssUri, sss.USER_SHEET);
} catch (ex) {}
var css = 'setting .preferences-alignment{ display:flex; flex-direction:row-reverse; align-items:center; }';
//var cssEnc = 'data:text/css;base64,' + window.btoa(css);
var cssEnc = encodeURIComponent(css);
var cssUri = makeURI('data:text/css,' + cssEnc);
sss.loadAndRegisterSheet(cssUri, sss.USER_SHEET);

replace makeURI with this:
function makeURI(aURL, aOriginCharset, aBaseURI)
{
return Services.io.newURI(aURL, aOriginCharset, aBaseURI);
}