--- a/dom/svg/nsSVGElement.cpp
+++ b/dom/svg/nsSVGElement.cpp
@@ -1126,26 +1126,49 @@ nsSVGElement::GetViewportElement()
 
 already_AddRefed<SVGAnimatedString>
 nsSVGElement::ClassName()
 {
   return mClassAttribute.ToDOMAnimatedString(this);
 }
 
 bool
-nsSVGElement::IsFocusableInternal(int32_t* aTabIndex, bool)
+nsSVGElement::IsSVGFocusable(bool* aIsFocusable, int32_t* aTabIndex)
 {
-  int32_t index = TabIndex();
-
-  if (index == -1) {
-    return false;
+  nsIDocument* doc = GetComposedDoc();
+  if (!doc || doc->HasFlag(NODE_IS_EDITABLE)) {
+    // In designMode documents we only allow focusing the document.
+    if (aTabIndex) {
+      *aTabIndex = -1;
+    }
+
+    *aIsFocusable = false;
+
+    return true;
   }
 
-  *aTabIndex = index;
-  return true;
+  int32_t tabIndex = TabIndex();
+
+  if (aTabIndex) {
+    *aTabIndex = tabIndex;
+  }
+
+  // If a tabindex is specified at all, or the default tabindex is 0, we're focusable
+  *aIsFocusable =
+    tabIndex >= 0 || HasAttr(kNameSpaceID_None, nsGkAtoms::tabindex);
+
+  return false;
+}
+
+bool
+nsSVGElement::IsFocusableInternal(int32_t* aTabIndex, bool aWithMouse)
+{
+  bool isFocusable = false;
+  IsSVGFocusable(&isFocusable, aTabIndex);
+  return isFocusable;
 }
 
 //------------------------------------------------------------------------
 // Helper class: MappedAttrParser, for parsing values of mapped attributes
 
 namespace {
 
 class MOZ_STACK_CLASS MappedAttrParser {

--- a/dom/svg/nsSVGElement.h
+++ b/dom/svg/nsSVGElement.h
@@ -313,16 +313,18 @@ public:
   virtual void ClearAnyCachedPath() {}
   virtual nsIDOMNode* AsDOMNode() final override { return this; }
   virtual bool IsTransformable() { return false; }
 
   // WebIDL
   mozilla::dom::SVGSVGElement* GetOwnerSVGElement();
   nsSVGElement* GetViewportElement();
   already_AddRefed<mozilla::dom::SVGAnimatedString> ClassName();
+
+  virtual bool IsSVGFocusable(bool* aIsFocusable, int32_t* aTabIndex);
   virtual bool IsFocusableInternal(int32_t* aTabIndex, bool aWithMouse) override;
 
 protected:
   virtual JSObject* WrapNode(JSContext *cx, JS::Handle<JSObject*> aGivenProto) override;
 
 #ifdef DEBUG
   // We define BeforeSetAttr here and mark it final to ensure it is NOT used
   // by SVG elements.