--- a/browser/base/content/tabbrowser.xml
+++ b/browser/base/content/tabbrowser.xml
@@ -4218,17 +4218,26 @@
                 let tabs = this.tabbrowser.mTabBox.tabs;
                 let tabPanel = this.tabbrowser.mPanelContainer;
                 let showPanel = tabs.getRelatedElement(showTab);
                 let index = Array.indexOf(tabPanel.childNodes, showPanel);
                 if (index != -1) {
                   this.log(`Switch to tab ${index} - ${this.tinfo(showTab)}`);
                   tabPanel.setAttribute("selectedIndex", index);
                   if (showTab === this.requestedTab) {
-                    this.tabbrowser._adjustFocusAfterTabSwitch(showTab);
+                    // It's possible for the tab we're switching to not be
+                    // focusable until later on this tick (example: it might be
+                    // pending). We ensure that the "select" event has had the
+                    // opportunity to fire by making sure that the focus adjustment
+                    // is one of the last things to occur.
+                    window.requestAnimationFrame(() => {
+                      if (this.visibleTab == showTab) {
+                        this.tabbrowser._adjustFocusAfterTabSwitch(showTab);
+                      }
+                    });
                   }
                 }
 
                 // This doesn't necessarily exist if we're a new window and haven't switched tabs yet
                 if (this.lastVisibleTab)
                   this.lastVisibleTab._visuallySelected = false;
 
                 this.visibleTab._visuallySelected = true;