Removed Firefox xhr_ulMultistream browser quirk because it was outdated

doc.md

@@ -367,7 +367,6 @@ __Advanced parameters:__ (Seriously, don't change these unless you know what you
 * __xhr_ulMultistream__: how many streams should be opened for the upload test
     * Default: `3`
     * Recommended: `>=1`
-    * Default override: 1 on Firefox if enable_quirks is true
 * __xhr_ul_blob_megabytes__: size in megabytes of the blobs sent during the upload test
 	* Default: `20`
 	* Default override: 4 on Chromium-based mobile browsers (limitation introduced around version 65). This will be forced

speedtest_worker.js

@@ -126,10 +126,6 @@ this.addEventListener("message", function(e) {
 			if (settings.enable_quirks || (typeof s.enable_quirks !== "undefined" && s.enable_quirks)) {
 				var ua = navigator.userAgent;
 				if (/Firefox.(\d+\.\d+)/i.test(ua)) {
-					if (typeof s.xhr_ulMultistream === "undefined") {
-						// ff more precise with 1 upload stream
-						settings.xhr_ulMultistream = 1;
-					}
 					if (typeof s.ping_allowPerformanceApi === "undefined") {
 						// ff performance API sucks
 						settings.ping_allowPerformanceApi = false;