Merge pull request #88 from mozilla/run-at-early

Add set-html-email.js worker a little earlier, so the loading message…

addon/background.js

@@ -123,6 +123,7 @@ async function sendEmail(tabIds) {
   let html = emailTemplates.renderEmail(tabIds.map(id => tabInfo[id]), TemplateComponent);
   await browser.tabs.executeScript(newTab.id, {
     file: "set-html-email.js",
+    runAt: "document_start",
   });
   await browser.tabs.sendMessage(newTab.id, {
     type: "setHtml",