Bug 1062128 - set tooltiptext for new tab button directly for a11y reasons, r=johannh

Differential Revision: https://phabricator.services.mozilla.com/D13406

--HG--
extra : moz-landing-system : lando

browser/base/content/browser.js

@@ -5912,8 +5912,7 @@ if (AppConstants.platform == "macosx") {
 }
 
 const gDynamicTooltipCache = new Map();
-function UpdateDynamicShortcutTooltipText(aTooltip) {
-  let nodeId = aTooltip.triggerNode.id || aTooltip.triggerNode.getAttribute("anonid");
+function GetDynamicShortcutTooltipText(nodeId) {
   if (!gDynamicTooltipCache.has(nodeId) && nodeId in nodeToTooltipMap) {
     let strId = nodeToTooltipMap[nodeId];
     let args = [];
@@ -5926,9 +5925,15 @@ function UpdateDynamicShortcutTooltipText(aTooltip) {
     }
     gDynamicTooltipCache.set(nodeId, gNavigatorBundle.getFormattedString(strId, args));
   }
-  aTooltip.setAttribute("label", gDynamicTooltipCache.get(nodeId));
+  return gDynamicTooltipCache.get(nodeId);
 }
 
+function UpdateDynamicShortcutTooltipText(aTooltip) {
+  let nodeId = aTooltip.triggerNode.id || aTooltip.triggerNode.getAttribute("anonid");
+  aTooltip.setAttribute("label", GetDynamicShortcutTooltipText(nodeId));
+}
+
+
 /*
  * - [ Dependencies ] ---------------------------------------------------------
  *  utilityOverlay.js:

browser/base/content/tabbrowser.xml

@@ -93,7 +93,7 @@
                            anonid="tabs-newtab-button"
                            command="cmd_newNavigatorTab"
                            onclick="checkForMiddleClick(this, event);"
-                           tooltip="dynamic-shortcut-tooltip"/>
+                           />
         <xul:spacer class="closing-tabs-spacer" anonid="closing-tabs-spacer"
                     style="width: 0;"/>
       </xul:arrowscrollbox>
@@ -112,6 +112,10 @@
           var tab = this.firstElementChild;
           tab.label = this.emptyTabTitle;
 
+          let newTabButton = document.getAnonymousElementByAttribute(
+            this, "anonid", "tabs-newtab-button");
+          newTabButton.setAttribute("tooltiptext", GetDynamicShortcutTooltipText("tabs-newtab-button"));
+
           window.addEventListener("resize", this);
 
           Services.prefs.addObserver("privacy.userContext", this);