radioGroupTabFocus

radioGroupTabFocus.patch

diff --git a/accessible/tests/mochitest/events/test_focus_controls.html b/accessible/tests/mochitest/events/test_focus_controls.html
index 268ec5d0e46b7..0760082ad94b3 100644
--- a/accessible/tests/mochitest/events/test_focus_controls.html
+++ b/accessible/tests/mochitest/events/test_focus_controls.html
@@ -31,7 +31,17 @@
       gQueue.push(new synthFocus("button2"));
       gQueue.push(new synthFocus("checkbox"));
       gQueue.push(new synthFocus("radio1"));
+      // Only the checked radio button is tabbable. If there's no checked radio
+      // button (as in this case), only the first radio button is tabbable.
+      gQueue.push(new synthTab("radio1", new nofocusChecker("radio2")));
+      // Shift+Tabbing from after a radiogroup should lead to the first radio
+      // button in the group if none is checked.
+      gQueue.push(new synthShiftTab("file", new focusChecker("radio1")));
       gQueue.push(new synthDownKey("radio1", new focusChecker("radio2")));
+      // Now the second radio button is checked, so it should be tabbable
+      // instead of the first.
+      gQueue.push(new synthFocus("checkbox"));
+      gQueue.push(new synthTab("checkbox", new focusChecker("radio2")));
 
       // no focus events for checkbox or radio inputs when they are checked
       // programmatically
diff --git a/dom/base/RadioGroupContainer.cpp b/dom/base/RadioGroupContainer.cpp
index 1d5abb78c6bc0..8217f110b03f4 100644
--- a/dom/base/RadioGroupContainer.cpp
+++ b/dom/base/RadioGroupContainer.cpp
@@ -131,6 +131,19 @@ nsresult RadioGroupContainer::GetNextRadioButton(
   return NS_OK;
 }
 
+nsresult RadioGroupContainer::GetFirstSelectableRadioButton(
+    const nsAString& aName, HTMLInputElement** aRadioOut) {
+  *aRadioOut = nullptr;
+  nsRadioGroupStruct* radioGroup = GetOrCreateRadioGroup(aName);
+  for (RefPtr<HTMLInputElement> radio : radioGroup->mRadioButtons.AsList()) {
+    if (!radio->Disabled()) {
+      radio.forget(aRadioOut);
+      break;
+    }
+  }
+  return NS_OK;
+}
+
 void RadioGroupContainer::AddToRadioGroup(const nsAString& aName,
                                           HTMLInputElement* aRadio,
                                           nsIContent* aAncestor) {
diff --git a/dom/base/RadioGroupContainer.h b/dom/base/RadioGroupContainer.h
index 0c920c1c09b7d..2e0649a6ce46e 100644
--- a/dom/base/RadioGroupContainer.h
+++ b/dom/base/RadioGroupContainer.h
@@ -32,6 +32,8 @@ class RadioGroupContainer final {
   nsresult GetNextRadioButton(const nsAString& aName, const bool aPrevious,
                               HTMLInputElement* aFocusedRadio,
                               HTMLInputElement** aRadioOut);
+  nsresult GetFirstSelectableRadioButton(const nsAString& aName,
+                                         HTMLInputElement** aRadioOut);
   void AddToRadioGroup(const nsAString& aName, HTMLInputElement* aRadio,
                        nsIContent* aAncestor);
   void RemoveFromRadioGroup(const nsAString& aName, HTMLInputElement* aRadio);
diff --git a/dom/html/HTMLInputElement.cpp b/dom/html/HTMLInputElement.cpp
index e52ceec22475e..a8cfc48e290ff 100644
--- a/dom/html/HTMLInputElement.cpp
+++ b/dom/html/HTMLInputElement.cpp
@@ -6482,8 +6482,6 @@ bool HTMLInputElement::IsHTMLFocusable(bool aWithMouse, bool* aIsFocusable,
     return false;
   }
 
-  // Current radio button is not selected.
-  // But make it tabbable if nothing in group is selected.
   auto* container = GetCurrentRadioGroupContainer();
   if (!container) {
     *aIsFocusable = defaultFocusable;
@@ -6493,8 +6491,17 @@ bool HTMLInputElement::IsHTMLFocusable(bool aWithMouse, bool* aIsFocusable,
   nsAutoString name;
   GetAttr(nsGkAtoms::name, name);
 
+  // Only the checked radio button (or the 1st, if none is checked) is tabbable.
   if (container->GetCurrentRadioButton(name)) {
     *aTabIndex = -1;
+    *aIsFocusable = defaultFocusable;
+    return false;
+  }
+
+  RefPtr<HTMLInputElement> firstRadio;
+  container->GetFirstSelectableRadioButton(name, getter_AddRefs(firstRadio));
+  if (this != firstRadio) {
+    *aTabIndex = -1;
   }
   *aIsFocusable = defaultFocusable;
   return false;