diff --git a/dom/base/nsGkAtomList.h b/dom/base/nsGkAtomList.h
index 1e9d870594..75c031afac 100644
--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -1134,6 +1134,7 @@ GK_ATOM(scrollbarDownBottom, "scrollbar-down-bottom")
 GK_ATOM(scrollbarDownTop, "scrollbar-down-top")
 GK_ATOM(scrollbarUpBottom, "scrollbar-up-bottom")
 GK_ATOM(scrollbarUpTop, "scrollbar-up-top")
+GK_ATOM(scrollbarwidth, "scrollbarwidth")
 GK_ATOM(scrollbox, "scrollbox")
 GK_ATOM(scrollcorner, "scrollcorner")
 GK_ATOM(scrolling, "scrolling")
diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index d1053da86d..e1a7215d93 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -4457,6 +4457,7 @@ ScrollFrameHelper::CreateAnonymousContent(
                                           kNameSpaceID_XUL,
                                           nsIDOMNode::ELEMENT_NODE);
   NS_ENSURE_TRUE(nodeInfo, NS_ERROR_OUT_OF_MEMORY);
+  StyleScrollbarWidth scrollWidth = mOuter->StyleUserInterface()->mScrollbarWidth;
 
   if (canHaveHorizontal) {
     RefPtr<NodeInfo> ni = nodeInfo;
@@ -4473,6 +4474,17 @@ ScrollFrameHelper::CreateAnonymousContent(
                                 NS_LITERAL_STRING("horizontal"), false);
     mHScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::clickthrough,
                                 NS_LITERAL_STRING("always"), false);
+    // Map scrollbar-width to an attribute for browser themes.
+    if (scrollWidth == StyleScrollbarWidth::None) {
+      mHScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::scrollbarwidth,
+                                  NS_LITERAL_STRING("none"), false);
+    } else if (scrollWidth == StyleScrollbarWidth::Thin) {
+      mHScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::scrollbarwidth,
+                                  NS_LITERAL_STRING("thin"), false);
+    } else {
+      mHScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::scrollbarwidth,
+                                  NS_LITERAL_STRING("auto"), false);
+    }
     if (mIsRoot) {
       mHScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::root_,
                                   NS_LITERAL_STRING("true"), false);
@@ -4496,6 +4508,17 @@ ScrollFrameHelper::CreateAnonymousContent(
                                 NS_LITERAL_STRING("vertical"), false);
     mVScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::clickthrough,
                                 NS_LITERAL_STRING("always"), false);
+    // Map scrollbar-width to an attribute for browser themes.
+    if (scrollWidth == StyleScrollbarWidth::None) {
+      mVScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::scrollbarwidth,
+                                  NS_LITERAL_STRING("none"), false);
+    } else if (scrollWidth == StyleScrollbarWidth::Thin) {
+      mVScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::scrollbarwidth,
+                                  NS_LITERAL_STRING("thin"), false);
+    } else {
+      mVScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::scrollbarwidth,
+                                  NS_LITERAL_STRING("auto"), false);
+    }
     if (mIsRoot) {
       mVScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::root_,
                                   NS_LITERAL_STRING("true"), false);