--- a/.lldbinit
+++ b/.lldbinit
@@ -4,8 +4,13 @@
 # single compiled file breaks lldb breakpoint setting. This works around that.
 # See http://lldb.llvm.org/troubleshooting.html for more info.
 settings set target.inline-breakpoint-strategy always
 
 # Show the dynamic type of an object when using "expr".  This, for example,
 # will show a variable declared as "nsIFrame *" that points to an nsBlockFrame
 # object as being of type "nsBlockFrame *" rather than "nsIFrame *".
 settings set target.prefer-dynamic-value run-target
+
+# Import the module that defines complex Gecko debugging commands.  Rather
+# than do any kind of searching, this assumes that you are running lldb from
+# the top level source directory.
+script sys.path.append('python/lldbutils'); import lldbutils; lldbutils.init()

--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -5370,16 +5370,22 @@ nsFrame::MakeFrameName(const nsAString& 
 
 void
 nsIFrame::DumpFrameTree()
 {
   RootFrameList(PresContext(), stdout, 0);
 }
 
 void
+nsIFrame::DumpFrameTreeLimited()
+{
+  List(stdout, 0);
+}
+
+void
 nsIFrame::RootFrameList(nsPresContext* aPresContext, FILE* out, int32_t aIndent)
 {
   if (!aPresContext || !out)
     return;
 
   nsIPresShell *shell = aPresContext->GetPresShell();
   if (shell) {
     nsIFrame* frame = shell->FrameManager()->GetRootFrame();

--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -3256,16 +3256,17 @@ public:
   virtual void List(FILE* out, int32_t aIndent, uint32_t aFlags = 0) const;
   /**
    * lists the frames beginning from the root frame
    * - calls root frame's List(...)
    */
   static void RootFrameList(nsPresContext* aPresContext,
                             FILE* out, int32_t aIndent);
   virtual void DumpFrameTree();
+  void DumpFrameTreeLimited();
 
   NS_IMETHOD  GetFrameName(nsAString& aResult) const = 0;
 #endif
 
 #ifdef DEBUG
 public:
   NS_IMETHOD_(nsFrameState)  GetDebugStateBits() const = 0;
   NS_IMETHOD  DumpRegressionData(nsPresContext* aPresContext,

new file mode 100644
--- /dev/null
+++ b/python/lldbutils/README.txt
@@ -0,0 +1,12 @@
+lldb debugging functionality for Gecko
+--------------------------------------
+
+This directory contains a module, lldbutils, which is imported by the
+in-tree .lldbinit file.  The lldbutil modules define some lldb commands
+that are handy for debugging Gecko.
+
+If you want to add a new command or Python-implemented type summary, either add
+it to one of the existing broad area Python files (such as lldbutils/layout.py
+for layout-related commands) or create a new file if none of the existing files
+is appropriate.  If you add a new file, make sure you add it to __all__ in
+lldbutils/__init__.py.

new file mode 100644
--- /dev/null
+++ b/python/lldbutils/lldbutils/__init__.py
@@ -0,0 +1,7 @@
+import lldb
+
+__all__ = ['layout']
+
+def init():
+    for name in __all__:
+        __import__('lldbutils.' + name, globals(), locals(), ['init']).init(lldb.debugger)

new file mode 100644
--- /dev/null
+++ b/python/lldbutils/lldbutils/layout.py
@@ -0,0 +1,15 @@
+import lldb
+
+def frametree(debugger, command, result, dict):
+    """Dumps the frame tree containing the given nsIFrame*."""
+    debugger.HandleCommand('expr (' + command + ')->DumpFrameTree()')
+
+def frametreelimited(debugger, command, result, dict):
+    """Dumps the subtree of a frame tree rooted at the given nsIFrame*."""
+    debugger.HandleCommand('expr (' + command + ')->DumpFrameTreeLimited()')
+
+def init(debugger):
+    debugger.HandleCommand('command script add -f lldbutils.layout.frametree frametree')
+    debugger.HandleCommand('command script add -f lldbutils.layout.frametree frametreelimited')
+    debugger.HandleCommand('command alias ft frametree')
+    debugger.HandleCommand('command alias ftl frametree')