Remove loop around XHR.

src/lib/SyncMessage.js

@@ -188,15 +188,13 @@
         // on Firefox we first need to send an async message telling the
         // background script about the tab ID, which does not get sent
         // with "privileged" XHR
-        let result, done = false;
+        let result;
         browser.runtime.sendMessage(
           {__syncMessage__: {id: msgId, payload: msg}}
         ).then(r => {
-          done = true;
           result = r;
           if (callback) callback(r);
         }).catch(e => {
-          done = true;
           throw e;
         });
 
@@ -209,7 +207,6 @@
         let suspend = () => {
           if (suspended) return;
           suspended = true;
-          while(!done) {
           try {
             let r = new XMLHttpRequest();
             r.open("GET", suspendURL, false);
@@ -217,7 +214,6 @@
           } catch (e) {
             console.error(e);
           }
-          }
           suspended = false;
         };
         let domSuspender = new MutationObserver(records => {