--- a/.lldbinit
+++ b/.lldbinit
@@ -1,10 +1,15 @@
 # .lldbinit file for debugging Mozilla
 
+# -----------------------------------------------------------------------------
+# For documentation on all of the commands and type summaries defined here
+# and in the accompanying Python scripts, see python/lldbutils/README.txt.
+# -----------------------------------------------------------------------------
+
 # Mozilla's use of UNIFIED_SOURCES to include multiple source files into a
 # 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 *".

--- a/python/lldbutils/README.txt
+++ b/python/lldbutils/README.txt
@@ -1,12 +1,189 @@
 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.
+
+
+Supported commands
+------------------
+
+Most commands below that can take a pointer to an object also support being
+called with a smart pointer like nsRefPtr or nsCOMPtr.
+
+
+* frametree EXPR, ft EXPR
+  frametreelimited EXPR, ftl EXPR
+
+  Shows information about a frame tree.  EXPR is an expression that
+  is evaluated, and must be an nsIFrame*.  frametree displays the
+  entire frame tree that contains the given frame.  frametreelimited
+  displays a subtree of the frame tree rooted at the given frame.
+
+  (lldb) p this
+  (nsBlockFrame *) $4 = 0x000000011687fcb8
+  (lldb) ftl this
+  Block(div)(-1)@0x11687fcb8 {0,0,7380,690} [state=0002100000d04601] [content=0x11688c0c0] [sc=0x11687f990:-moz-scrolled-content]<
+    line 0x116899130: count=1 state=inline,clean,prevmarginclean,not impacted,not wrapped,before:nobr,after:nobr[0x100] {60,0,0,690} vis-overflow=60,510,0,0 scr-overflow=60,510,0,0 <
+      Text(0)""@0x1168990c0 {60,510,0,0} [state=0001000020404000] [content=0x11687ca10] [sc=0x11687fd88:-moz-non-element,parent=0x11687eb00] [run=0x115115e80][0,0,T]
+    >
+  >
+  (lldb) ft this
+  Viewport(-1)@0x116017430 [view=0x115efe190] {0,0,60,60} [state=000b063000002623] [sc=0x1160170f8:-moz-viewport]<
+    HTMLScroll(html)(-1)@0x1160180d0 {0,0,0,0} [state=000b020000000403] [content=0x115e4d640] [sc=0x116017768:-moz-viewport-scroll]<
+      ...
+      Canvas(html)(-1)@0x116017e08 {0,0,60,60} vis-overflow=0,0,8340,2196 scr-overflow=0,0,8220,2196 [state=000b002000000601] [content=0x115e4d640] [sc=0x11687e0f8:-moz-scrolled-canvas]<
+        Block(html)(-1)@0x11687e578 {0,0,60,2196} vis-overflow=0,0,8340,2196 scr-overflow=0,0,8220,2196 [state=000b100000d00601] [content=0x115e4d640] [sc=0x11687e4b8,parent=0x0]<
+          line 0x11687ec48: count=1 state=block,clean,prevmarginclean,not impacted,not wrapped,before:nobr,after:nobr[0x48] bm=480 {480,480,0,1236} vis-overflow=360,426,7980,1410 scr-overflow=480,480,7740,1236 <
+            Block(body)(1)@0x11687ebb0 {480,480,0,1236} vis-overflow=-120,-54,7980,1410 scr-overflow=0,0,7740,1236 [state=000b120000100601] [content=0x115ed8980] [sc=0x11687e990]<
+              line 0x116899170: count=1 state=inline,clean,prevmarginclean,not impacted,not wrapped,before:nobr,after:nobr[0x0] {0,0,7740,1236} vis-overflow=-120,-54,7980,1410 scr-overflow=0,0,7740,1236 <
+                nsTextControlFrame@0x11687f068 {0,66,7740,1170} vis-overflow=-120,-120,7980,1410 scr-overflow=0,0,7740,1170 [state=0002000000004621] [content=0x115ca2c50] [sc=0x11687ea40]<
+                  HTMLScroll(div)(-1)@0x11687f6b0 {180,240,7380,690} [state=0002000000084409] [content=0x11688c0c0] [sc=0x11687eb00]<
+                    Block(div)(-1)@0x11687fcb8 {0,0,7380,690} [state=0002100000d04601] [content=0x11688c0c0] [sc=0x11687f990:-moz-scrolled-content]<
+                      line 0x116899130: count=1 state=inline,clean,prevmarginclean,not impacted,not wrapped,before:nobr,after:nobr[0x100] {60,0,0,690} vis-overflow=60,510,0,0 scr-overflow=60,510,0,0 <
+                        Text(0)""@0x1168990c0 {60,510,0,0} [state=0001000020404000] [content=0x11687ca10] [sc=0x11687fd88:-moz-non-element,parent=0x11687eb00] [run=0x115115e80][0,0,T]
+ ...
+
+
+* js
+
+  Dumps the current JS stack.
+
+  (lldb) js
+  0 anonymous(aForce = false) ["chrome://browser/content/browser.js":13414]
+      this = [object Object]
+  1 updateAppearance() ["chrome://browser/content/browser.js":13326]
+      this = [object Object]
+  2 handleEvent(aEvent = [object Event]) ["chrome://browser/content/tabbrowser.xml":3811]
+      this = [object XULElement]
+
+
+* prefcnt EXPR
+
+  Shows the refcount of a given object.  EXPR is an expression that is
+  evaluated, and can be either a pointer to or an actual refcounted
+  object.  The object can be a standard nsISupports-like refcounted
+  object, a cycle-collected object or a mozilla::RefCounted<T> object.
+
+  (lldb) p this
+  (nsHTMLDocument *) $1 = 0x0000000116e9d800
+  (lldb) prefcnt this
+  20
+  (lldb) p mDocumentURI
+  (nsCOMPtr<nsIURI>) $3 = {
+    mRawPtr = 0x0000000117163e50
+  }
+  (lldb) prefcnt mDocumentURI
+  11
+
+
+* ptag EXPR
+
+  Shows the DOM tag name of a node.  EXPR is an expression that is
+  evaluated, and can be either an nsINode pointer or a concrete DOM
+  object.
+
+  (lldb) p this
+  (nsHTMLDocument *) $0 = 0x0000000116e9d800
+  (lldb) ptag this
+  (PermanentAtomImpl *) $1 = 0x0000000110133ac0 u"#document"
+  (lldb) p this->GetRootElement()
+  (mozilla::dom::HTMLSharedElement *) $2 = 0x0000000118429780
+  (lldb) ptag $2
+  (PermanentAtomImpl *) $3 = 0x0000000110123b80 u"html"
+
+
+Supported type summaries and synthetic children
+-----------------------------------------------
+
+In lldb terminology, type summaries are rules for how to display a value
+when using the "expression" command (or its familiar-to-gdb-users "p" alias),
+and synthetic children are fake member variables or array elements also
+added by custom rules.
+
+For objects that do have synthetic children defined for them, like nsTArray,
+the "expr -R -- EXPR" command can be used to show its actual member variables.
+
+
+* nsAString, nsACString
+
+  Strings have a type summary that shows the actual string.
+
+  (lldb) frame info
+  frame #0: 0x000000010400cfea XUL`nsCSSParser::ParseProperty(this=0x00007fff5fbf5248, aPropID=eCSSProperty_margin_top, aPropValue=0x00007fff5fbf53f8, aSheetURI=0x0000000115ae8c00, aBaseURI=0x0000000115ae8c00, aSheetPrincipal=0x000000010ff9e040, aDeclaration=0x00000001826fd580, aChanged=0x00007fff5fbf5247, aIsImportant=false, aIsSVGMode=false) + 74 at nsCSSParser.cpp:12851
+  (lldb) p aPropValue
+  (const nsAString_internal) $16 = u"-25px"
+
+  (lldb) p this
+  (nsHTMLDocument *) $18 = 0x0000000115b56000
+  (lldb) p mContentType
+  (nsCString) $19 = {
+    nsACString_internal = "text/html"
+  }
+
+* nsIAtom
+
+  Atoms have a type summary that shows the string value inside the atom.
+
+  (lldb) frame info
+  frame #0: 0x00000001028b8c49 XUL`mozilla::dom::Element::GetBoolAttr(this=0x0000000115ca1c50, aAttr=0x000000011012a640) const + 25 at Element.h:907
+  (lldb) p aAttr
+  (PermanentAtomImpl *) $1 = 0x000000011012a640 u"readonly"
+
+* nsTArray and friends
+
+  nsTArrays and their auto and fallible varieties have synthetic children
+  for their elements.  This means when displaying them with "expr" (or "p"),
+  they will be shown like regular arrays, rather than showing the mHdr and
+  other fields.
+
+  (lldb) frame info
+  frame #0: 0x00000001043eb8a8 XUL`SVGTextFrame::DoGlyphPositioning(this=0x000000012f3f8778) + 248 at SVGTextFrame.cpp:4940
+  (lldb) p charPositions
+  (nsTArray<nsPoint>) $5 = {
+    [0] = {
+      mozilla::gfx::BasePoint<int, nsPoint> = {
+        x = 0
+        y = 816
+      }
+    }
+    [1] = {
+      mozilla::gfx::BasePoint<int, nsPoint> = {
+        x = 426
+        y = 816
+      }
+    }
+    [2] = {
+      mozilla::gfx::BasePoint<int, nsPoint> = {
+        x = 906
+        y = 816
+      }
+    }
+  }
+  (lldb) expr -R -- charPositions
+  (nsTArray<nsPoint>) $4 = {
+    nsTArray_Impl<nsPoint, nsTArrayInfallibleAllocator> = {
+      nsTArray_base<nsTArrayInfallibleAllocator, nsTArray_CopyWithMemutils> = {
+        mHdr = 0x000000012f3f1b80
+      }
+    }
+  }
+
+* nsTextNode, nsTextFragment
+
+  Text nodes have a type summary that shows the nsTextFragment in the
+  nsTextNode, which itself has a type summary that shows the text
+  content.
+
+  (lldb) p this
+  (nsTextFrame *) $14 = 0x000000011811bb10
+  (lldb) p mContent
+  (nsTextNode *) $15 = 0x0000000118130110 "Search or enter address"
+