diff --git a/content/base/src/nsRuleNode.cpp b/content/base/src/nsRuleNode.cpp
index 6c68e9ee233..063722bc61a 100644
--- a/content/base/src/nsRuleNode.cpp
+++ b/content/base/src/nsRuleNode.cpp
@@ -416,9 +416,9 @@ nsRuleNode::Destroy()
   mPresContext->FreeToShell(sizeof(nsRuleNode), this);
 }
 
-void nsRuleNode::CreateRootNode(nsIPresContext* aPresContext, nsRuleNode** aResult)
+nsRuleNode* nsRuleNode::CreateRootNode(nsIPresContext* aPresContext)
 {
-  *aResult = new (aPresContext) nsRuleNode(aPresContext);
+  return new (aPresContext) nsRuleNode(aPresContext, nsnull, nsnull);
 }
 
 nsILanguageAtomService* nsRuleNode::gLangService = nsnull;
@@ -555,6 +555,8 @@ nsRuleNode::PathContainsRule(nsIStyleRule* aRule, PRBool* aMatched)
 nsresult
 nsRuleNode::ClearCachedData(nsIStyleRule* aRule)
 {
+  NS_ASSERTION(aRule, "you should be using ClearCachedDataInSubtree");
+
   nsRuleNode* ruleDest = this;
   while (ruleDest) {
     if (ruleDest->mRule == aRule)
@@ -563,6 +565,8 @@ nsRuleNode::ClearCachedData(nsIStyleRule* aRule)
   }
 
   if (ruleDest) {
+    NS_ASSERTION(ruleDest->mParent, "node must not be root");
+
     // The rule was contained along our branch.  We need to blow away
     // all cached data along this path.  Note that, because of the definition
     // of inline style, all nodes along this path must have exactly one child.  This
@@ -603,8 +607,10 @@ nsRuleNode::ClearCachedDataInSubtree(nsIStyleRule* aRule)
     // We have a match.  Blow away all data stored at this node.
     if (mStyleData.mResetData || mStyleData.mInheritedData)
       mStyleData.Destroy(0, mPresContext);
+
     mNoneBits &= ~NS_STYLE_INHERIT_MASK;
     mDependentBits &= ~NS_STYLE_INHERIT_MASK;
+
     aRule = nsnull;  // Cause everything to be blown away in the descendants.
   }
 
@@ -980,7 +986,7 @@ static const PropertyCheckData SVGCheckProperties[] = {
   
 static const StructCheckData gCheckProperties[] = {
 
-#define STYLE_STRUCT(name, checkdata_cb) \
+#define STYLE_STRUCT(name, checkdata_cb, ctor_args) \
   {name##CheckProperties, \
    sizeof(name##CheckProperties)/sizeof(PropertyCheckData), \
    checkdata_cb},
@@ -1608,16 +1614,6 @@ nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
   return res;
 }
 
-static nscoord
-ZoomFont(nsIPresContext* aPresContext, nscoord aInSize)
-{
-  nsCOMPtr<nsIDeviceContext> dc;
-  aPresContext->GetDeviceContext(getter_AddRefs(dc));
-  float textZoom;
-  dc->GetTextZoom(textZoom);
-  return nscoord(aInSize * textZoom);
-}
-
 static PRBool
 IsChrome(nsIPresContext* aPresContext)
 {
@@ -1643,10 +1639,7 @@ nsRuleNode::SetDefaultOnRoot(const nsStyleStructID aSID, nsStyleContext* aContex
   switch (aSID) {
     case eStyleStruct_Font: 
     {
-      const nsFont* defaultFont;
-      mPresContext->GetDefaultFont(kPresContext_DefaultVariableFont_ID, &defaultFont);
-      nsStyleFont* fontData = new (mPresContext) nsStyleFont(*defaultFont);
-      fontData->mSize = ZoomFont(mPresContext, fontData->mFont.size);
+      nsStyleFont* fontData = new (mPresContext) nsStyleFont(mPresContext);
 
       nscoord minimumFontSize = 0;
       mPresContext->GetCachedIntPref(kPresContext_MinimumFontSize, minimumFontSize);
@@ -1792,7 +1785,7 @@ nsRuleNode::SetDefaultOnRoot(const nsStyleStructID aSID, nsStyleContext* aContex
 nsRuleNode::ComputeStyleDataFn
 nsRuleNode::gComputeStyleDataFn[] = {
 
-#define STYLE_STRUCT(name, checkdata_cb) \
+#define STYLE_STRUCT(name, checkdata_cb, ctor_args) \
   &nsRuleNode::Compute##name##Data,
 #include "nsStyleStructList.h"
 #undef STYLE_STRUCT
@@ -1805,7 +1798,7 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
         nscoord aMinFontSize, PRBool aUseDocumentFonts, PRBool aChromeOverride,
         PRBool aIsGeneric, const nsRuleDataFont& aFontData,
         const nsFont& aDefaultFont, const nsStyleFont* aParentFont,
-        nsStyleFont* aFont, PRBool aZoom, PRBool& aInherited)
+        nsStyleFont* aFont, PRBool& aInherited)
 {
   const nsFont* defaultVariableFont;
   const nsFont* defaultFixedFont;
@@ -1863,7 +1856,9 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
       if (NS_FAILED(dc->GetSystemFont(sysID, &aFont->mFont))) {
         aFont->mFont.name = defaultVariableFont->name;
       }
-      aFont->mSize = aFont->mFont.size; // this becomes our cascading size
+      // this becomes our cascading size
+      aFont->mSize = aFont->mFont.size
+          = nsStyleFont::ZoomText(aPresContext, aFont->mFont.size);
     }
 
     aFont->mFont.familyNameQuirks = PR_FALSE;
@@ -1964,7 +1959,7 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
   }
 
   // font-size: enum, length, percent, inherit
-  PRBool zoom = aZoom;
+  PRBool zoom = PR_FALSE;
   if (eCSSUnit_Enumerated == aFontData.mSize.GetUnit()) {
     PRInt32 value = aFontData.mSize.GetIntValue();
     PRInt32 scaler;
@@ -1987,12 +1982,8 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
 
       // Un-zoom so we use the tables correctly.  We'll then rezoom due
       // to the |zoom = PR_TRUE| above.
-      nsCOMPtr<nsIDeviceContext> dc;
-      aPresContext->GetDeviceContext(getter_AddRefs(dc));
-      float textZoom;
-      dc->GetTextZoom(textZoom);
-
-      nscoord parentSize = nscoord(aParentFont->mSize / textZoom);
+      nscoord parentSize =
+          nsStyleFont::UnZoomText(aPresContext, aParentFont->mSize);
 
       if (NS_STYLE_FONT_SIZE_LARGER == value) {
         PRInt32 index = nsStyleUtil::FindNextLargerFontSize(parentSize, (PRInt32)aDefaultFont.size,
@@ -2058,7 +2049,7 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
   // We want to zoom the cascaded size so that em-based measurements,
   // line-heights, etc., work.
   if (zoom)
-    aFont->mSize = ZoomFont(aPresContext, aFont->mSize);
+    aFont->mSize = nsStyleFont::ZoomText(aPresContext, aFont->mSize);
 
   // enforce the user' specified minimum font-size on the value that we expose
   if (aChromeOverride) {
@@ -2116,8 +2107,9 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
   const nsFont* defaultFont;
   aPresContext->GetDefaultFont(aGenericFontID, &defaultFont);
   nsStyleFont parentFont(*defaultFont);
+  parentFont.mSize = parentFont.mFont.size
+      = nsStyleFont::ZoomText(aPresContext, parentFont.mSize);
   PRInt32 i = contextPath.Count() - 1;
-  PRBool zoom = PR_TRUE;
   if (higherContext) {
     nsStyleContext* context = (nsStyleContext*)contextPath[i];
     nsStyleFont* tmpFont = (nsStyleFont*)context->GetStyleData(eStyleStruct_Font);
@@ -2125,7 +2117,6 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
     parentFont.mFont = tmpFont->mFont;
     parentFont.mSize = tmpFont->mSize;
     --i;
-    zoom = PR_FALSE;
   }
   aFont->mFlags = parentFont.mFlags;
   aFont->mFont = parentFont.mFont;
@@ -2163,7 +2154,7 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
 
     SetFont(aPresContext, context, aMinFontSize,
             aUseDocumentFonts, aChromeOverride, PR_TRUE,
-            fontData, *defaultFont, &parentFont, aFont, zoom, dummy);
+            fontData, *defaultFont, &parentFont, aFont, dummy);
 
     // XXX Not sure if we need to do this here
     // If we have a post-resolve callback, handle that now.
@@ -2173,7 +2164,6 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
     parentFont.mFlags = aFont->mFlags;
     parentFont.mFont = aFont->mFont;
     parentFont.mSize = aFont->mSize;
-    zoom = PR_FALSE;
   }
 
   // Finish off by applying our own rules. In this case, aFontData
@@ -2181,7 +2171,7 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
   // can just compute the delta from the parent.
   SetFont(aPresContext, aContext, aMinFontSize,
           aUseDocumentFonts, aChromeOverride, PR_TRUE,
-          aFontData, *defaultFont, &parentFont, aFont, zoom, dummy);
+          aFontData, *defaultFont, &parentFont, aFont, dummy);
 }
 
 const nsStyleStruct* 
@@ -2222,12 +2212,8 @@ nsRuleNode::ComputeFontData(nsStyleStruct* aStartStruct,
     }
   }
 
-  PRBool zoom = PR_FALSE;
-  const nsFont* defaultFont;
   if (!font) {
-    mPresContext->GetDefaultFont(kPresContext_DefaultVariableFont_ID, &defaultFont);
-    font = new (mPresContext) nsStyleFont(*defaultFont);
-    zoom = PR_TRUE;
+    font = new (mPresContext) nsStyleFont(mPresContext);
   }
   if (!parentFont)
     parentFont = font;
@@ -2268,6 +2254,8 @@ nsRuleNode::ComputeFontData(nsStyleStruct* aStartStruct,
   // determine if we have to override the minimum font-size constraint.
   if (!useDocumentFonts || minimumFontSize > 0) {
     chromeOverride = IsChrome(mPresContext);
+    // XXXldb Just fix up |useDocumentFonts| here and drop the
+    // |chromeOverride| variable from here on!
   }
 
   // If we don't have to use document fonts, then we are only entitled
@@ -2282,10 +2270,11 @@ nsRuleNode::ComputeFontData(nsStyleStruct* aStartStruct,
     // continue the normal processing
     // our default font is the most recent generic font
     generic = parentFont->mFlags & NS_STYLE_FONT_FACE_MASK;
+    const nsFont* defaultFont;
     mPresContext->GetDefaultFont(generic, &defaultFont);
     SetFont(mPresContext, aContext, minimumFontSize,
             useDocumentFonts, chromeOverride, PR_FALSE,
-            fontData, *defaultFont, parentFont, font, zoom, inherited);
+            fontData, *defaultFont, parentFont, font, inherited);
   }
   else {
     // re-calculate the font as a generic font
@@ -2368,8 +2357,8 @@ nsRuleNode::ComputeTextData(nsStyleStruct* aStartStruct,
              aContext, mPresContext, inherited);
     if (textData.mLineHeight.IsFixedLengthUnit() ||
         textData.mLineHeight.GetUnit() == eCSSUnit_Pixel)
-      text->mLineHeight.SetCoordValue(
-                    ZoomFont(mPresContext, text->mLineHeight.GetCoordValue()));
+      text->mLineHeight.SetCoordValue(nsStyleFont::ZoomText(mPresContext,
+                                           text->mLineHeight.GetCoordValue()));
   }
 
 
@@ -4637,24 +4626,31 @@ nsRuleNode::ComputeSVGData(nsStyleStruct* aStartStruct,
 inline const nsStyleStruct* 
 nsRuleNode::GetParentData(const nsStyleStructID aSID)
 {
-  nsRuleNode* ruleNode = mParent;
-  nsStyleStruct* currStruct = nsnull;
-  while (ruleNode) {
-    currStruct = ruleNode->mStyleData.GetStyleData(aSID);
-    if (currStruct)
-      break; // We found a rule with fully specified data.  We don't need to go up
-             // the tree any further, since the remainder of this branch has already
-             // been computed.
-    ruleNode = ruleNode->mParent; // Climb up to the next rule in the tree (a less specific rule).
-  }  
+  // Walk up the rule tree from this rule node (towards less specific
+  // rules).
+  for (nsRuleNode* ruleNode = mParent; ruleNode; ruleNode = ruleNode->mParent)
+  {
+    const nsStyleStruct *currStruct = ruleNode->mStyleData.GetStyleData(aSID);
+    if (currStruct) {
+      // We found a rule with fully specified data.  We don't need to go
+      // up the tree any further, since the remainder of this branch has
+      // already been computed.
+      return currStruct;
+    }
+    NS_ASSERTION(ruleNode->mDependentBits &
+                 nsCachedStyleData::GetBitForSID(aSID),
+                 "dependent bits improperly set");
+  }
 
-  return currStruct; // Just return whatever we found.
+  NS_NOTREACHED("dependent bits set on root or improperly set");
+  return nsnull;
 }
 
 nsRuleNode::GetStyleDataFn
 nsRuleNode::gGetStyleDataFn[] = {
 
-#define STYLE_STRUCT(name, checkdata_cb) &nsRuleNode::Get##name##Data,
+#define STYLE_STRUCT(name, checkdata_cb, ctor_args) \
+  &nsRuleNode::Get##name##Data,
 #include "nsStyleStructList.h"
 #undef STYLE_STRUCT
 
@@ -4666,21 +4662,42 @@ nsRuleNode::GetStyleData(nsStyleStructID aSID,
                          nsStyleContext* aContext,
                          PRBool aComputeData)
 {
-  const nsStyleStruct* cachedData = mStyleData.GetStyleData(aSID);
-  if (cachedData)
-    return cachedData; // We have a fully specified struct. Just return it.
+  const nsStyleStruct* data = mStyleData.GetStyleData(aSID);
+  if (data)
+    return data; // We have a fully specified struct. Just return it.
 
-  if (mDependentBits & nsCachedStyleData::GetBitForSID(aSID))
-    return GetParentData(aSID); // We depend on an ancestor for this
-                                // struct since the cached struct it has
-                                // is also appropriate for this rule
-                                // node.  Just go up the rule tree and
-                                // return the first cached struct we
-                                // find.
+  if (mDependentBits & nsCachedStyleData::GetBitForSID(aSID)) {
+    // We depend on an ancestor for this struct since the cached struct
+    // it has is also appropriate for this rule node.  Just go up the
+    // rule tree and return the first cached struct we find.
+    data = GetParentData(aSID);
+    if (data)
+      return data;
+    NS_NOTREACHED("dependent bits set but no cached struct present");
+  }
 
   // Nothing is cached.  We'll have to delve further and examine our rules.
   GetStyleDataFn fn = gGetStyleDataFn[aSID];
-  return fn ? (this->*fn)(aContext, aComputeData) : nsnull;
+  if (!fn) {
+    NS_NOTREACHED("unknown style struct requested");
+    return nsnull;
+  }
+  data = (this->*fn)(aContext, aComputeData);
+  if (data || !aComputeData)
+    return data;
+
+  NS_NOTREACHED("could not create style struct");
+  // To ensure that |GetStyleData| never returns null (even when we're
+  // out of memory), we'll get the style set and get a copy of the
+  // default values for the given style struct from the set.  Note that
+  // this works fine even if |this| is a rule node that has been
+  // destroyed (leftover from a previous rule tree) but is somehow still
+  // used.
+  nsCOMPtr<nsIPresShell> shell;
+  mPresContext->GetShell(getter_AddRefs(shell));
+  nsCOMPtr<nsIStyleSet> set;
+  shell->GetStyleSet(getter_AddRefs(set));
+  return set->GetDefaultStyleData()->GetStyleData(aSID);
 }
 
 void
diff --git a/content/base/src/nsStyleSet.cpp b/content/base/src/nsStyleSet.cpp
index e2a2aee206e..606c4474433 100644
--- a/content/base/src/nsStyleSet.cpp
+++ b/content/base/src/nsStyleSet.cpp
@@ -189,6 +189,10 @@ public:
   virtual nsresult BeginRuleTreeReconstruct();
   virtual nsresult EndRuleTreeReconstruct();
   
+  // For getting the cached default data in case we hit out-of-memory.
+  // To be used only by nsRuleNode.
+  virtual nsCachedStyleData* GetDefaultStyleData();
+
   virtual nsresult GetRuleTree(nsRuleNode** aResult);
   virtual nsresult ClearCachedDataInRuleTree(nsIStyleRule* aRule);
   
@@ -319,6 +323,9 @@ protected:
   
   void EnsureRuleWalker(nsIPresContext* aPresContext);
 
+  // Returns false on out-of-memory.
+  PRBool BuildDefaultStyleData(nsIPresContext* aPresContext);
+
   void ClearRuleProcessors(void);
   void ClearAgentRuleProcessors(void);
   void ClearUserRuleProcessors(void);
@@ -365,6 +372,11 @@ protected:
 
   nsCOMPtr<nsIStyleRuleSupplier> mStyleRuleSupplier; 
 
+  // To be used only in case of emergency, such as being out of memory
+  // or operating on a deleted rule node.  The latter should never
+  // happen, of course.
+  nsCachedStyleData mDefaultStyleData;
+
   nsRuleNode* mRuleTree; // This is the root of our rule tree.  It is a lexicographic tree of
                          // matched rules that style contexts use to look up properties.
   nsRuleNode* mOldRuleTree; // Used during rule tree reconstruction.
@@ -1143,25 +1155,55 @@ StyleSetImpl::WalkRuleProcessors(nsISupportsArrayEnumFunc aFunc,
     mOverrideRuleProcessors->EnumerateForwards(aFunc, aData);
 }
 
-#ifdef NS_DEBUG
-#define NS_ASSERT_REFCOUNT(ptr,cnt,msg) { \
-  nsrefcnt  count = ptr->AddRef();        \
-  ptr->Release();                         \
-  NS_ASSERTION(--count == cnt, msg);      \
-}
-#else
-#define NS_ASSERT_REFCOUNT(ptr,cnt,msg) {}
-#endif
-
 void StyleSetImpl::EnsureRuleWalker(nsIPresContext* aPresContext)
-{ 
+{
   if (mRuleWalker)
     return;
 
-  nsRuleNode::CreateRootNode(aPresContext, &mRuleTree);
+  if (!mDefaultStyleData.mResetData && !BuildDefaultStyleData(aPresContext)) {
+    mDefaultStyleData.Destroy(0, aPresContext);
+    return;
+  }
+
+  mRuleTree = nsRuleNode::CreateRootNode(aPresContext);
+  if (!mRuleTree)
+    return;
   mRuleWalker = new nsRuleWalker(mRuleTree);
 }
 
+PRBool StyleSetImpl::BuildDefaultStyleData(nsIPresContext* aPresContext)
+{
+  NS_ASSERTION(!mDefaultStyleData.mResetData &&
+               !mDefaultStyleData.mInheritedData,
+               "leaking default style data");
+  mDefaultStyleData.mResetData = new (aPresContext) nsResetStyleData;
+  if (!mDefaultStyleData.mResetData)
+    return PR_FALSE;
+  mDefaultStyleData.mInheritedData = new (aPresContext) nsInheritedStyleData;
+  if (!mDefaultStyleData.mInheritedData)
+    return PR_FALSE;
+
+#define SSARG_PRESCONTEXT aPresContext
+
+#define CREATE_DATA(name, type, args) \
+  if (!(mDefaultStyleData.m##type##Data->m##name##Data = \
+          new (aPresContext) nsStyle##name args)) \
+    return PR_FALSE;
+
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
+  CREATE_DATA(name, Inherited, ctor_args)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
+  CREATE_DATA(name, Reset, ctor_args)
+
+#include "nsStyleStructList.h"
+
+#undef STYLE_STRUCT_INHERITED
+#undef STYLE_STRUCT_RESET
+#undef SSARG_PRESCONTEXT
+
+  return PR_TRUE;
+}
+
 already_AddRefed<nsStyleContext>
 StyleSetImpl::ResolveStyleFor(nsIPresContext* aPresContext,
                               nsIContent* aContent,
@@ -1184,6 +1226,7 @@ StyleSetImpl::ResolveStyleFor(nsIPresContext* aPresContext,
         mDocRuleProcessors   ||
         mOverrideRuleProcessors) {
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       nsCOMPtr<nsIAtom> medium;
       aPresContext->GetMedium(getter_AddRefs(medium));
       RulesMatchingData data(aPresContext, medium, aContent, mRuleWalker);
@@ -1218,6 +1261,7 @@ StyleSetImpl::ResolveStyleForNonElement(nsIPresContext* aPresContext,
         mDocRuleProcessors   ||
         mOverrideRuleProcessors) {
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       result = GetContext(aPresContext, aParentContext,
                           nsCSSAnonBoxes::mozNonElement).get();
       NS_ASSERTION(mRuleWalker->AtRoot(), "rule walker must be at root");
@@ -1282,6 +1326,7 @@ StyleSetImpl::ResolvePseudoStyleFor(nsIPresContext* aPresContext,
       nsCOMPtr<nsIAtom> medium;
       aPresContext->GetMedium(getter_AddRefs(medium));
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       PseudoRulesMatchingData data(aPresContext, medium, aParentContent, 
                                    aPseudoTag, aComparator, mRuleWalker);
       FileRules(EnumPseudoRulesMatching, &data);
@@ -1324,6 +1369,7 @@ StyleSetImpl::ProbePseudoStyleFor(nsIPresContext* aPresContext,
       nsCOMPtr<nsIAtom> medium;
       aPresContext->GetMedium(getter_AddRefs(medium));
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       PseudoRulesMatchingData data(aPresContext, medium, aParentContent, 
                                    aPseudoTag, nsnull, mRuleWalker);
       FileRules(EnumPseudoRulesMatching, &data);
@@ -1378,11 +1424,15 @@ NS_IMETHODIMP
 StyleSetImpl::Shutdown(nsIPresContext* aPresContext)
 {
   delete mRuleWalker;
+  mRuleWalker = nsnull;
   if (mRuleTree)
   {
     mRuleTree->Destroy();
     mRuleTree = nsnull;
   }
+
+  mDefaultStyleData.Destroy(0, aPresContext);
+
   return NS_OK;
 }
 
@@ -1450,6 +1500,12 @@ StyleSetImpl::EndRuleTreeReconstruct()
   return NS_OK;
 }
 
+nsCachedStyleData*
+StyleSetImpl::GetDefaultStyleData()
+{
+  return &mDefaultStyleData;
+}
+
 nsresult
 StyleSetImpl::ClearCachedDataInRuleTree(nsIStyleRule* aInlineStyleRule)
 {
@@ -1507,6 +1563,7 @@ StyleSetImpl::ReParentStyleContext(nsIPresContext* aPresContext,
       nsRuleNode* ruleNode;
       aStyleContext->GetRuleNode(&ruleNode);
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       mRuleWalker->SetCurrentNode(ruleNode);
 
       already_AddRefed<nsStyleContext> result =
@@ -1845,14 +1902,9 @@ void StyleSetImpl::ListContexts(nsIFrame* aRootFrame, FILE* out, PRInt32 aIndent
 nsresult
 NS_NewStyleSet(nsIStyleSet** aInstancePtrResult)
 {
-  if (!aInstancePtrResult) {
-    return NS_ERROR_NULL_POINTER;
-  }
-
-  StyleSetImpl  *it = new StyleSetImpl();
-  if (!it) {
+  StyleSetImpl *it = new StyleSetImpl();
+  if (!it)
     return NS_ERROR_OUT_OF_MEMORY;
-  }
 
   return CallQueryInterface(it, aInstancePtrResult);
 }
diff --git a/content/html/style/src/nsStyleUtil.cpp b/content/html/style/src/nsStyleUtil.cpp
index 08ab6fcd701..4b16eee665b 100644
--- a/content/html/style/src/nsStyleUtil.cpp
+++ b/content/html/style/src/nsStyleUtil.cpp
@@ -66,11 +66,11 @@
 nsCachedStyleData::StyleStructInfo
 nsCachedStyleData::gInfo[] = {
 
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
   { offsetof(nsCachedStyleData, mInheritedData), \
     offsetof(nsInheritedStyleData, m##name##Data), \
     PR_FALSE },
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
   { offsetof(nsCachedStyleData, mResetData), \
     offsetof(nsResetStyleData, m##name##Data), \
     PR_TRUE },
diff --git a/content/shared/public/nsRuleNode.h b/content/shared/public/nsRuleNode.h
index 20ef5a05826..1ffe935fef0 100644
--- a/content/shared/public/nsRuleNode.h
+++ b/content/shared/public/nsRuleNode.h
@@ -57,9 +57,9 @@ typedef void (*nsPostResolveFunc)(nsStyleStruct* aStyleStruct, nsRuleData* aData
 struct nsInheritedStyleData
 {
 
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
   nsStyle##name * m##name##Data;
-#define STYLE_STRUCT_RESET(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -73,10 +73,10 @@ struct nsInheritedStyleData
   };
 
   void ClearInheritedData(PRUint32 aBits) {
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
     if (m##name##Data && (aBits & NS_STYLE_INHERIT_BIT(name))) \
       m##name##Data = nsnull;
-#define STYLE_STRUCT_RESET(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -85,10 +85,10 @@ struct nsInheritedStyleData
   };
 
   void Destroy(PRUint32 aBits, nsIPresContext* aContext) {
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
     if (m##name##Data && !(aBits & NS_STYLE_INHERIT_BIT(name))) \
       m##name##Data->Destroy(aContext);
-#define STYLE_STRUCT_RESET(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -99,9 +99,9 @@ struct nsInheritedStyleData
   };
 
   nsInheritedStyleData() {
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
     m##name##Data = nsnull;
-#define STYLE_STRUCT_RESET(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -115,9 +115,9 @@ struct nsResetStyleData
 {
   nsResetStyleData()
   {
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
     m##name##Data = nsnull;
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -132,10 +132,10 @@ struct nsResetStyleData
   }
 
   void ClearInheritedData(PRUint32 aBits) {
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
     if (m##name##Data && (aBits & NS_STYLE_INHERIT_BIT(name))) \
       m##name##Data = nsnull;
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -144,10 +144,10 @@ struct nsResetStyleData
   };
 
   void Destroy(PRUint32 aBits, nsIPresContext* aContext) {
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
     if (m##name##Data && !(aBits & NS_STYLE_INHERIT_BIT(name))) \
       m##name##Data->Destroy(aContext);
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -157,9 +157,9 @@ struct nsResetStyleData
     aContext->FreeToShell(sizeof(nsResetStyleData), this);
   };
 
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
   nsStyle##name * m##name##Data;
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -542,10 +542,11 @@ protected:
   static GetStyleDataFn gGetStyleDataFn[];
 
 public:
-  nsRuleNode(nsIPresContext* aPresContext, nsIStyleRule* aRule=nsnull, nsRuleNode* aParent=nsnull);
+  nsRuleNode(nsIPresContext* aPresContext, nsIStyleRule* aRule,
+             nsRuleNode* aParent);
   virtual ~nsRuleNode();
 
-  static void CreateRootNode(nsIPresContext* aPresContext, nsRuleNode** aResult);
+  static nsRuleNode* CreateRootNode(nsIPresContext* aPresContext);
 
   nsresult GetBits(PRInt32 aType, PRUint32* aResult);
   nsresult Transition(nsIStyleRule* aRule, nsRuleNode** aResult);
diff --git a/content/shared/public/nsStyleContext.h b/content/shared/public/nsStyleContext.h
index 061237bacb9..1ff1e4c6351 100644
--- a/content/shared/public/nsStyleContext.h
+++ b/content/shared/public/nsStyleContext.h
@@ -98,7 +98,27 @@ public:
    */
   void Mark();
 
+  /*
+   * Get the style data for a style struct.  This is the most important
+   * member function of nsIStyleContext.  It fills in a const pointer
+   * to a style data struct that is appropriate for the style context's
+   * frame.  This struct may be shared with other contexts (either in
+   * the rule tree or the style context tree), so it should not be
+   * modified.
+   *
+   * This function will NOT return null (even when out of memory) when
+   * given a valid style struct ID, so the result does not need to be
+   * null-checked.
+   *
+   * The typesafe global helper function |GetStyleData| (below) is
+   * preferred to the use of this function (and is a simple typesafe
+   * wrapper for this function).
+   *
+   * See also |nsIFrame::GetStyleData| and the other global
+   * |GetStyleData| in nsIFrame.h.
+   */
   const nsStyleStruct* GetStyleData(nsStyleStructID aSID);
+
   const nsStyleStruct* PeekStyleData(nsStyleStructID aSID);
 
   nsStyleStruct* GetUniqueStyleData(nsIPresContext* aPresContext, const nsStyleStructID& aSID);
diff --git a/content/shared/public/nsStyleStruct.h b/content/shared/public/nsStyleStruct.h
index 7af7e4a4456..11111feaa75 100644
--- a/content/shared/public/nsStyleStruct.h
+++ b/content/shared/public/nsStyleStruct.h
@@ -64,7 +64,7 @@ enum nsStyleStructID {
  * increase by 1.
  */
 
-#define STYLE_STRUCT(name, checkdata_cb) eStyleStruct_##name,
+#define STYLE_STRUCT(name, checkdata_cb, ctor_args) eStyleStruct_##name,
 #include "nsStyleStructList.h"
 #undef STYLE_STRUCT
 
@@ -96,12 +96,18 @@ struct nsStyleStruct {
 
 struct nsStyleFont : public nsStyleStruct {
   nsStyleFont(void);
+  nsStyleFont(const nsFont& aFont);
+  nsStyleFont(const nsStyleFont& aStyleFont);
+  nsStyleFont(nsIPresContext *aPresContext);
   ~nsStyleFont(void) {};
 
   NS_DEFINE_STATIC_STYLESTRUCTID_ACCESSOR(eStyleStruct_Font)
 
   nsChangeHint CalcDifference(const nsStyleFont& aOther) const;
   static nsChangeHint CalcFontDifference(const nsFont& aFont1, const nsFont& aFont2);
+
+  static nscoord ZoomText(nsIPresContext* aPresContext, nscoord aSize);
+  static nscoord UnZoomText(nsIPresContext* aPresContext, nscoord aSize);
   
   void* operator new(size_t sz, nsIPresContext* aContext) CPP_THROW_NEW;
   void Destroy(nsIPresContext* aContext);
@@ -112,10 +118,6 @@ struct nsStyleFont : public nsStyleStruct {
                         // which is our "actual size" and is enforced to be >= the user's
                         // preferred min-size. mFont.size should be used for display purposes
                         // while mSize is the value to return in getComputedStyle() for example.
-
-  nsStyleFont(const nsFont& aFont);
-  nsStyleFont(const nsStyleFont& aStyleFont);
-  nsStyleFont(nsIPresContext* aPresContext);
 };
 
 struct nsStyleColor : public nsStyleStruct {
diff --git a/content/shared/public/nsStyleStructList.h b/content/shared/public/nsStyleStructList.h
index f57734d1099..a16ab996ee2 100644
--- a/content/shared/public/nsStyleStructList.h
+++ b/content/shared/public/nsStyleStructList.h
@@ -44,40 +44,41 @@
  */
 
 #ifndef STYLE_STRUCT_INHERITED
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
-  STYLE_STRUCT(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
+  STYLE_STRUCT(name, checkdata_cb, ctor_args)
 #define UNDEF_STYLE_STRUCT_INHERITED
 #endif
 
 #ifndef STYLE_STRUCT_RESET
-#define STYLE_STRUCT_RESET(name, checkdata_cb) STYLE_STRUCT(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
+  STYLE_STRUCT(name, checkdata_cb, ctor_args)
 #define UNDEF_STYLE_STRUCT_RESET
 #endif
 
-STYLE_STRUCT_INHERITED(Font, CheckFontCallback)
-STYLE_STRUCT_INHERITED(Color, nsnull)
-STYLE_STRUCT_RESET(Background, nsnull)
-STYLE_STRUCT_INHERITED(List, nsnull)
-STYLE_STRUCT_RESET(Position, nsnull)
-STYLE_STRUCT_INHERITED(Text, nsnull)
-STYLE_STRUCT_RESET(TextReset, nsnull)
-STYLE_STRUCT_RESET(Display, nsnull)
-STYLE_STRUCT_INHERITED(Visibility, nsnull)
-STYLE_STRUCT_RESET(Content, nsnull)
-STYLE_STRUCT_INHERITED(Quotes, nsnull)
-STYLE_STRUCT_INHERITED(UserInterface, nsnull)
-STYLE_STRUCT_RESET(UIReset, nsnull)
-STYLE_STRUCT_RESET(Table, nsnull)
-STYLE_STRUCT_INHERITED(TableBorder, nsnull)
-STYLE_STRUCT_RESET(Margin, nsnull)
-STYLE_STRUCT_RESET(Padding, nsnull)
-STYLE_STRUCT_RESET(Border, nsnull)
-STYLE_STRUCT_RESET(Outline, nsnull)
+STYLE_STRUCT_INHERITED(Font, CheckFontCallback, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_INHERITED(Color, nsnull, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_RESET(Background, nsnull, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_INHERITED(List, nsnull, ())
+STYLE_STRUCT_RESET(Position, nsnull, ())
+STYLE_STRUCT_INHERITED(Text, nsnull, ())
+STYLE_STRUCT_RESET(TextReset, nsnull, ())
+STYLE_STRUCT_RESET(Display, nsnull, ())
+STYLE_STRUCT_INHERITED(Visibility, nsnull, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_RESET(Content, nsnull, ())
+STYLE_STRUCT_INHERITED(Quotes, nsnull, ())
+STYLE_STRUCT_INHERITED(UserInterface, nsnull, ())
+STYLE_STRUCT_RESET(UIReset, nsnull, ())
+STYLE_STRUCT_RESET(Table, nsnull, ())
+STYLE_STRUCT_INHERITED(TableBorder, nsnull, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_RESET(Margin, nsnull, ())
+STYLE_STRUCT_RESET(Padding, nsnull, ())
+STYLE_STRUCT_RESET(Border, nsnull, ())
+STYLE_STRUCT_RESET(Outline, nsnull, (SSARG_PRESCONTEXT))
 #ifdef INCLUDE_XUL
-STYLE_STRUCT_RESET(XUL, nsnull)
+STYLE_STRUCT_RESET(XUL, nsnull, ())
 #endif
 #ifdef MOZ_SVG
-STYLE_STRUCT_INHERITED(SVG, nsnull)
+STYLE_STRUCT_INHERITED(SVG, nsnull, ())
 #endif
 
 #ifdef UNDEF_STYLE_STRUCT_INHERITED
diff --git a/content/shared/src/nsStyleStruct.cpp b/content/shared/src/nsStyleStruct.cpp
index 2ab1fa3fc69..83f06dbdac1 100644
--- a/content/shared/src/nsStyleStruct.cpp
+++ b/content/shared/src/nsStyleStruct.cpp
@@ -42,6 +42,7 @@
 #include "nsString.h"
 #include "nsUnitConversion.h"
 #include "nsIPresContext.h"
+#include "nsIDeviceContext.h"
 #include "nsIStyleRule.h"
 #include "nsISupportsArray.h"
 #include "nsCRT.h"
@@ -230,6 +231,17 @@ nsStyleFont::nsStyleFont(const nsStyleFont& aSrc)
 {
 }
 
+
+nsStyleFont::nsStyleFont(nsIPresContext* aPresContext)
+  : mFlags(NS_STYLE_FONT_DEFAULT)
+{
+  const nsFont* defaultFont;
+  aPresContext->GetDefaultFont(kPresContext_DefaultVariableFont_ID,
+                               &defaultFont);
+  mFont = *defaultFont;
+  mSize = mFont.size = nsStyleFont::ZoomText(aPresContext, mFont.size);
+}
+
 void* 
 nsStyleFont::operator new(size_t sz, nsIPresContext* aContext) CPP_THROW_NEW {
   void* result = nsnull;
@@ -253,6 +265,28 @@ nsChangeHint nsStyleFont::CalcDifference(const nsStyleFont& aOther) const
   return NS_STYLE_HINT_REFLOW;
 }
 
+inline float
+TextZoomFor(nsIPresContext* aPresContext)
+{
+  nsCOMPtr<nsIDeviceContext> dc;
+  aPresContext->GetDeviceContext(getter_AddRefs(dc));
+  float textZoom;
+  dc->GetTextZoom(textZoom);
+  return textZoom;
+}
+
+/* static */ nscoord
+nsStyleFont::ZoomText(nsIPresContext *aPresContext, nscoord aSize)
+{
+  return nscoord(float(aSize) * TextZoomFor(aPresContext));
+}
+
+/* static */ nscoord
+nsStyleFont::UnZoomText(nsIPresContext *aPresContext, nscoord aSize)
+{
+  return nscoord(float(aSize) / TextZoomFor(aPresContext));
+}
+
 nsChangeHint nsStyleFont::CalcFontDifference(const nsFont& aFont1, const nsFont& aFont2)
 {
   if ((aFont1.size == aFont2.size) && 
@@ -1004,6 +1038,8 @@ nsChangeHint nsStyleBackground::CalcDifference(const nsStyleBackground& aOther)
     && ((NS_STYLE_BG_ATTACHMENT_FIXED == mBackgroundAttachment) ||
         (NS_STYLE_BG_ATTACHMENT_FIXED == aOther.mBackgroundAttachment)))
     // this might require creation of a view
+    // XXX This probably doesn't call ApplyRenderingChangeToTree, which
+    // means we might not invalidate the canvas if this is the body.
     return NS_STYLE_HINT_FRAMECHANGE;
 
   if ((mBackgroundAttachment == aOther.mBackgroundAttachment) &&
diff --git a/layout/base/public/nsIFrame.h b/layout/base/public/nsIFrame.h
index 089d99b6bda..a689c25dbdd 100644
--- a/layout/base/public/nsIFrame.h
+++ b/layout/base/public/nsIFrame.h
@@ -579,7 +579,12 @@ public:
   NS_IMETHOD DidSetStyleContext(nsIPresContext* aPresContext) = 0;
 
   /**
-   * Get the style data associated with this frame.
+   * Get the style data associated with this frame.  This fills in a
+   * const style struct pointer that should never be modified.  See
+   * |nsIStyleContext::GetStyleData| for more information.
+   *
+   * The use of the typesafe global helper function |GetStyleData|,
+   * below, is preferred to direct use of this function.
    */
   NS_IMETHOD GetStyleDataExternal(nsStyleStructID aSID,
                                   const nsStyleStruct*& aStyleStruct) const = 0;
diff --git a/layout/base/public/nsIStyleSet.h b/layout/base/public/nsIStyleSet.h
index 94ebceaa910..259da145f7b 100644
--- a/layout/base/public/nsIStyleSet.h
+++ b/layout/base/public/nsIStyleSet.h
@@ -58,6 +58,7 @@ class nsIFrameManager;
 class nsISupportsArray;
 class nsRuleNode;
 struct nsFindFrameHint;
+struct nsCachedStyleData;
 
 #include "nsVoidArray.h"
 
@@ -125,6 +126,10 @@ public:
   virtual nsresult BeginRuleTreeReconstruct()=0;
   virtual nsresult EndRuleTreeReconstruct()=0;
 
+  // For getting the cached default data in case we hit out-of-memory.
+  // To be used only by nsRuleNode.
+  virtual nsCachedStyleData* GetDefaultStyleData() = 0;
+
   virtual nsresult GetStyleFrameConstruction(nsIStyleFrameConstruction** aResult) = 0;
 
   // ClearCachedStyleData is used to invalidate portions of both the style context tree
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index 089d99b6bda..a689c25dbdd 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -579,7 +579,12 @@ public:
   NS_IMETHOD DidSetStyleContext(nsIPresContext* aPresContext) = 0;
 
   /**
-   * Get the style data associated with this frame.
+   * Get the style data associated with this frame.  This fills in a
+   * const style struct pointer that should never be modified.  See
+   * |nsIStyleContext::GetStyleData| for more information.
+   *
+   * The use of the typesafe global helper function |GetStyleData|,
+   * below, is preferred to direct use of this function.
    */
   NS_IMETHOD GetStyleDataExternal(nsStyleStructID aSID,
                                   const nsStyleStruct*& aStyleStruct) const = 0;
diff --git a/layout/style/nsRuleNode.cpp b/layout/style/nsRuleNode.cpp
index 6c68e9ee233..063722bc61a 100644
--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -416,9 +416,9 @@ nsRuleNode::Destroy()
   mPresContext->FreeToShell(sizeof(nsRuleNode), this);
 }
 
-void nsRuleNode::CreateRootNode(nsIPresContext* aPresContext, nsRuleNode** aResult)
+nsRuleNode* nsRuleNode::CreateRootNode(nsIPresContext* aPresContext)
 {
-  *aResult = new (aPresContext) nsRuleNode(aPresContext);
+  return new (aPresContext) nsRuleNode(aPresContext, nsnull, nsnull);
 }
 
 nsILanguageAtomService* nsRuleNode::gLangService = nsnull;
@@ -555,6 +555,8 @@ nsRuleNode::PathContainsRule(nsIStyleRule* aRule, PRBool* aMatched)
 nsresult
 nsRuleNode::ClearCachedData(nsIStyleRule* aRule)
 {
+  NS_ASSERTION(aRule, "you should be using ClearCachedDataInSubtree");
+
   nsRuleNode* ruleDest = this;
   while (ruleDest) {
     if (ruleDest->mRule == aRule)
@@ -563,6 +565,8 @@ nsRuleNode::ClearCachedData(nsIStyleRule* aRule)
   }
 
   if (ruleDest) {
+    NS_ASSERTION(ruleDest->mParent, "node must not be root");
+
     // The rule was contained along our branch.  We need to blow away
     // all cached data along this path.  Note that, because of the definition
     // of inline style, all nodes along this path must have exactly one child.  This
@@ -603,8 +607,10 @@ nsRuleNode::ClearCachedDataInSubtree(nsIStyleRule* aRule)
     // We have a match.  Blow away all data stored at this node.
     if (mStyleData.mResetData || mStyleData.mInheritedData)
       mStyleData.Destroy(0, mPresContext);
+
     mNoneBits &= ~NS_STYLE_INHERIT_MASK;
     mDependentBits &= ~NS_STYLE_INHERIT_MASK;
+
     aRule = nsnull;  // Cause everything to be blown away in the descendants.
   }
 
@@ -980,7 +986,7 @@ static const PropertyCheckData SVGCheckProperties[] = {
   
 static const StructCheckData gCheckProperties[] = {
 
-#define STYLE_STRUCT(name, checkdata_cb) \
+#define STYLE_STRUCT(name, checkdata_cb, ctor_args) \
   {name##CheckProperties, \
    sizeof(name##CheckProperties)/sizeof(PropertyCheckData), \
    checkdata_cb},
@@ -1608,16 +1614,6 @@ nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
   return res;
 }
 
-static nscoord
-ZoomFont(nsIPresContext* aPresContext, nscoord aInSize)
-{
-  nsCOMPtr<nsIDeviceContext> dc;
-  aPresContext->GetDeviceContext(getter_AddRefs(dc));
-  float textZoom;
-  dc->GetTextZoom(textZoom);
-  return nscoord(aInSize * textZoom);
-}
-
 static PRBool
 IsChrome(nsIPresContext* aPresContext)
 {
@@ -1643,10 +1639,7 @@ nsRuleNode::SetDefaultOnRoot(const nsStyleStructID aSID, nsStyleContext* aContex
   switch (aSID) {
     case eStyleStruct_Font: 
     {
-      const nsFont* defaultFont;
-      mPresContext->GetDefaultFont(kPresContext_DefaultVariableFont_ID, &defaultFont);
-      nsStyleFont* fontData = new (mPresContext) nsStyleFont(*defaultFont);
-      fontData->mSize = ZoomFont(mPresContext, fontData->mFont.size);
+      nsStyleFont* fontData = new (mPresContext) nsStyleFont(mPresContext);
 
       nscoord minimumFontSize = 0;
       mPresContext->GetCachedIntPref(kPresContext_MinimumFontSize, minimumFontSize);
@@ -1792,7 +1785,7 @@ nsRuleNode::SetDefaultOnRoot(const nsStyleStructID aSID, nsStyleContext* aContex
 nsRuleNode::ComputeStyleDataFn
 nsRuleNode::gComputeStyleDataFn[] = {
 
-#define STYLE_STRUCT(name, checkdata_cb) \
+#define STYLE_STRUCT(name, checkdata_cb, ctor_args) \
   &nsRuleNode::Compute##name##Data,
 #include "nsStyleStructList.h"
 #undef STYLE_STRUCT
@@ -1805,7 +1798,7 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
         nscoord aMinFontSize, PRBool aUseDocumentFonts, PRBool aChromeOverride,
         PRBool aIsGeneric, const nsRuleDataFont& aFontData,
         const nsFont& aDefaultFont, const nsStyleFont* aParentFont,
-        nsStyleFont* aFont, PRBool aZoom, PRBool& aInherited)
+        nsStyleFont* aFont, PRBool& aInherited)
 {
   const nsFont* defaultVariableFont;
   const nsFont* defaultFixedFont;
@@ -1863,7 +1856,9 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
       if (NS_FAILED(dc->GetSystemFont(sysID, &aFont->mFont))) {
         aFont->mFont.name = defaultVariableFont->name;
       }
-      aFont->mSize = aFont->mFont.size; // this becomes our cascading size
+      // this becomes our cascading size
+      aFont->mSize = aFont->mFont.size
+          = nsStyleFont::ZoomText(aPresContext, aFont->mFont.size);
     }
 
     aFont->mFont.familyNameQuirks = PR_FALSE;
@@ -1964,7 +1959,7 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
   }
 
   // font-size: enum, length, percent, inherit
-  PRBool zoom = aZoom;
+  PRBool zoom = PR_FALSE;
   if (eCSSUnit_Enumerated == aFontData.mSize.GetUnit()) {
     PRInt32 value = aFontData.mSize.GetIntValue();
     PRInt32 scaler;
@@ -1987,12 +1982,8 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
 
       // Un-zoom so we use the tables correctly.  We'll then rezoom due
       // to the |zoom = PR_TRUE| above.
-      nsCOMPtr<nsIDeviceContext> dc;
-      aPresContext->GetDeviceContext(getter_AddRefs(dc));
-      float textZoom;
-      dc->GetTextZoom(textZoom);
-
-      nscoord parentSize = nscoord(aParentFont->mSize / textZoom);
+      nscoord parentSize =
+          nsStyleFont::UnZoomText(aPresContext, aParentFont->mSize);
 
       if (NS_STYLE_FONT_SIZE_LARGER == value) {
         PRInt32 index = nsStyleUtil::FindNextLargerFontSize(parentSize, (PRInt32)aDefaultFont.size,
@@ -2058,7 +2049,7 @@ SetFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
   // We want to zoom the cascaded size so that em-based measurements,
   // line-heights, etc., work.
   if (zoom)
-    aFont->mSize = ZoomFont(aPresContext, aFont->mSize);
+    aFont->mSize = nsStyleFont::ZoomText(aPresContext, aFont->mSize);
 
   // enforce the user' specified minimum font-size on the value that we expose
   if (aChromeOverride) {
@@ -2116,8 +2107,9 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
   const nsFont* defaultFont;
   aPresContext->GetDefaultFont(aGenericFontID, &defaultFont);
   nsStyleFont parentFont(*defaultFont);
+  parentFont.mSize = parentFont.mFont.size
+      = nsStyleFont::ZoomText(aPresContext, parentFont.mSize);
   PRInt32 i = contextPath.Count() - 1;
-  PRBool zoom = PR_TRUE;
   if (higherContext) {
     nsStyleContext* context = (nsStyleContext*)contextPath[i];
     nsStyleFont* tmpFont = (nsStyleFont*)context->GetStyleData(eStyleStruct_Font);
@@ -2125,7 +2117,6 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
     parentFont.mFont = tmpFont->mFont;
     parentFont.mSize = tmpFont->mSize;
     --i;
-    zoom = PR_FALSE;
   }
   aFont->mFlags = parentFont.mFlags;
   aFont->mFont = parentFont.mFont;
@@ -2163,7 +2154,7 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
 
     SetFont(aPresContext, context, aMinFontSize,
             aUseDocumentFonts, aChromeOverride, PR_TRUE,
-            fontData, *defaultFont, &parentFont, aFont, zoom, dummy);
+            fontData, *defaultFont, &parentFont, aFont, dummy);
 
     // XXX Not sure if we need to do this here
     // If we have a post-resolve callback, handle that now.
@@ -2173,7 +2164,6 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
     parentFont.mFlags = aFont->mFlags;
     parentFont.mFont = aFont->mFont;
     parentFont.mSize = aFont->mSize;
-    zoom = PR_FALSE;
   }
 
   // Finish off by applying our own rules. In this case, aFontData
@@ -2181,7 +2171,7 @@ SetGenericFont(nsIPresContext* aPresContext, nsStyleContext* aContext,
   // can just compute the delta from the parent.
   SetFont(aPresContext, aContext, aMinFontSize,
           aUseDocumentFonts, aChromeOverride, PR_TRUE,
-          aFontData, *defaultFont, &parentFont, aFont, zoom, dummy);
+          aFontData, *defaultFont, &parentFont, aFont, dummy);
 }
 
 const nsStyleStruct* 
@@ -2222,12 +2212,8 @@ nsRuleNode::ComputeFontData(nsStyleStruct* aStartStruct,
     }
   }
 
-  PRBool zoom = PR_FALSE;
-  const nsFont* defaultFont;
   if (!font) {
-    mPresContext->GetDefaultFont(kPresContext_DefaultVariableFont_ID, &defaultFont);
-    font = new (mPresContext) nsStyleFont(*defaultFont);
-    zoom = PR_TRUE;
+    font = new (mPresContext) nsStyleFont(mPresContext);
   }
   if (!parentFont)
     parentFont = font;
@@ -2268,6 +2254,8 @@ nsRuleNode::ComputeFontData(nsStyleStruct* aStartStruct,
   // determine if we have to override the minimum font-size constraint.
   if (!useDocumentFonts || minimumFontSize > 0) {
     chromeOverride = IsChrome(mPresContext);
+    // XXXldb Just fix up |useDocumentFonts| here and drop the
+    // |chromeOverride| variable from here on!
   }
 
   // If we don't have to use document fonts, then we are only entitled
@@ -2282,10 +2270,11 @@ nsRuleNode::ComputeFontData(nsStyleStruct* aStartStruct,
     // continue the normal processing
     // our default font is the most recent generic font
     generic = parentFont->mFlags & NS_STYLE_FONT_FACE_MASK;
+    const nsFont* defaultFont;
     mPresContext->GetDefaultFont(generic, &defaultFont);
     SetFont(mPresContext, aContext, minimumFontSize,
             useDocumentFonts, chromeOverride, PR_FALSE,
-            fontData, *defaultFont, parentFont, font, zoom, inherited);
+            fontData, *defaultFont, parentFont, font, inherited);
   }
   else {
     // re-calculate the font as a generic font
@@ -2368,8 +2357,8 @@ nsRuleNode::ComputeTextData(nsStyleStruct* aStartStruct,
              aContext, mPresContext, inherited);
     if (textData.mLineHeight.IsFixedLengthUnit() ||
         textData.mLineHeight.GetUnit() == eCSSUnit_Pixel)
-      text->mLineHeight.SetCoordValue(
-                    ZoomFont(mPresContext, text->mLineHeight.GetCoordValue()));
+      text->mLineHeight.SetCoordValue(nsStyleFont::ZoomText(mPresContext,
+                                           text->mLineHeight.GetCoordValue()));
   }
 
 
@@ -4637,24 +4626,31 @@ nsRuleNode::ComputeSVGData(nsStyleStruct* aStartStruct,
 inline const nsStyleStruct* 
 nsRuleNode::GetParentData(const nsStyleStructID aSID)
 {
-  nsRuleNode* ruleNode = mParent;
-  nsStyleStruct* currStruct = nsnull;
-  while (ruleNode) {
-    currStruct = ruleNode->mStyleData.GetStyleData(aSID);
-    if (currStruct)
-      break; // We found a rule with fully specified data.  We don't need to go up
-             // the tree any further, since the remainder of this branch has already
-             // been computed.
-    ruleNode = ruleNode->mParent; // Climb up to the next rule in the tree (a less specific rule).
-  }  
+  // Walk up the rule tree from this rule node (towards less specific
+  // rules).
+  for (nsRuleNode* ruleNode = mParent; ruleNode; ruleNode = ruleNode->mParent)
+  {
+    const nsStyleStruct *currStruct = ruleNode->mStyleData.GetStyleData(aSID);
+    if (currStruct) {
+      // We found a rule with fully specified data.  We don't need to go
+      // up the tree any further, since the remainder of this branch has
+      // already been computed.
+      return currStruct;
+    }
+    NS_ASSERTION(ruleNode->mDependentBits &
+                 nsCachedStyleData::GetBitForSID(aSID),
+                 "dependent bits improperly set");
+  }
 
-  return currStruct; // Just return whatever we found.
+  NS_NOTREACHED("dependent bits set on root or improperly set");
+  return nsnull;
 }
 
 nsRuleNode::GetStyleDataFn
 nsRuleNode::gGetStyleDataFn[] = {
 
-#define STYLE_STRUCT(name, checkdata_cb) &nsRuleNode::Get##name##Data,
+#define STYLE_STRUCT(name, checkdata_cb, ctor_args) \
+  &nsRuleNode::Get##name##Data,
 #include "nsStyleStructList.h"
 #undef STYLE_STRUCT
 
@@ -4666,21 +4662,42 @@ nsRuleNode::GetStyleData(nsStyleStructID aSID,
                          nsStyleContext* aContext,
                          PRBool aComputeData)
 {
-  const nsStyleStruct* cachedData = mStyleData.GetStyleData(aSID);
-  if (cachedData)
-    return cachedData; // We have a fully specified struct. Just return it.
+  const nsStyleStruct* data = mStyleData.GetStyleData(aSID);
+  if (data)
+    return data; // We have a fully specified struct. Just return it.
 
-  if (mDependentBits & nsCachedStyleData::GetBitForSID(aSID))
-    return GetParentData(aSID); // We depend on an ancestor for this
-                                // struct since the cached struct it has
-                                // is also appropriate for this rule
-                                // node.  Just go up the rule tree and
-                                // return the first cached struct we
-                                // find.
+  if (mDependentBits & nsCachedStyleData::GetBitForSID(aSID)) {
+    // We depend on an ancestor for this struct since the cached struct
+    // it has is also appropriate for this rule node.  Just go up the
+    // rule tree and return the first cached struct we find.
+    data = GetParentData(aSID);
+    if (data)
+      return data;
+    NS_NOTREACHED("dependent bits set but no cached struct present");
+  }
 
   // Nothing is cached.  We'll have to delve further and examine our rules.
   GetStyleDataFn fn = gGetStyleDataFn[aSID];
-  return fn ? (this->*fn)(aContext, aComputeData) : nsnull;
+  if (!fn) {
+    NS_NOTREACHED("unknown style struct requested");
+    return nsnull;
+  }
+  data = (this->*fn)(aContext, aComputeData);
+  if (data || !aComputeData)
+    return data;
+
+  NS_NOTREACHED("could not create style struct");
+  // To ensure that |GetStyleData| never returns null (even when we're
+  // out of memory), we'll get the style set and get a copy of the
+  // default values for the given style struct from the set.  Note that
+  // this works fine even if |this| is a rule node that has been
+  // destroyed (leftover from a previous rule tree) but is somehow still
+  // used.
+  nsCOMPtr<nsIPresShell> shell;
+  mPresContext->GetShell(getter_AddRefs(shell));
+  nsCOMPtr<nsIStyleSet> set;
+  shell->GetStyleSet(getter_AddRefs(set));
+  return set->GetDefaultStyleData()->GetStyleData(aSID);
 }
 
 void
diff --git a/layout/style/nsRuleNode.h b/layout/style/nsRuleNode.h
index 20ef5a05826..1ffe935fef0 100644
--- a/layout/style/nsRuleNode.h
+++ b/layout/style/nsRuleNode.h
@@ -57,9 +57,9 @@ typedef void (*nsPostResolveFunc)(nsStyleStruct* aStyleStruct, nsRuleData* aData
 struct nsInheritedStyleData
 {
 
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
   nsStyle##name * m##name##Data;
-#define STYLE_STRUCT_RESET(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -73,10 +73,10 @@ struct nsInheritedStyleData
   };
 
   void ClearInheritedData(PRUint32 aBits) {
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
     if (m##name##Data && (aBits & NS_STYLE_INHERIT_BIT(name))) \
       m##name##Data = nsnull;
-#define STYLE_STRUCT_RESET(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -85,10 +85,10 @@ struct nsInheritedStyleData
   };
 
   void Destroy(PRUint32 aBits, nsIPresContext* aContext) {
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
     if (m##name##Data && !(aBits & NS_STYLE_INHERIT_BIT(name))) \
       m##name##Data->Destroy(aContext);
-#define STYLE_STRUCT_RESET(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -99,9 +99,9 @@ struct nsInheritedStyleData
   };
 
   nsInheritedStyleData() {
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
     m##name##Data = nsnull;
-#define STYLE_STRUCT_RESET(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -115,9 +115,9 @@ struct nsResetStyleData
 {
   nsResetStyleData()
   {
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
     m##name##Data = nsnull;
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -132,10 +132,10 @@ struct nsResetStyleData
   }
 
   void ClearInheritedData(PRUint32 aBits) {
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
     if (m##name##Data && (aBits & NS_STYLE_INHERIT_BIT(name))) \
       m##name##Data = nsnull;
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -144,10 +144,10 @@ struct nsResetStyleData
   };
 
   void Destroy(PRUint32 aBits, nsIPresContext* aContext) {
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
     if (m##name##Data && !(aBits & NS_STYLE_INHERIT_BIT(name))) \
       m##name##Data->Destroy(aContext);
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -157,9 +157,9 @@ struct nsResetStyleData
     aContext->FreeToShell(sizeof(nsResetStyleData), this);
   };
 
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
   nsStyle##name * m##name##Data;
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args)
 
 #include "nsStyleStructList.h"
 
@@ -542,10 +542,11 @@ protected:
   static GetStyleDataFn gGetStyleDataFn[];
 
 public:
-  nsRuleNode(nsIPresContext* aPresContext, nsIStyleRule* aRule=nsnull, nsRuleNode* aParent=nsnull);
+  nsRuleNode(nsIPresContext* aPresContext, nsIStyleRule* aRule,
+             nsRuleNode* aParent);
   virtual ~nsRuleNode();
 
-  static void CreateRootNode(nsIPresContext* aPresContext, nsRuleNode** aResult);
+  static nsRuleNode* CreateRootNode(nsIPresContext* aPresContext);
 
   nsresult GetBits(PRInt32 aType, PRUint32* aResult);
   nsresult Transition(nsIStyleRule* aRule, nsRuleNode** aResult);
diff --git a/layout/style/nsStyleContext.h b/layout/style/nsStyleContext.h
index 061237bacb9..1ff1e4c6351 100644
--- a/layout/style/nsStyleContext.h
+++ b/layout/style/nsStyleContext.h
@@ -98,7 +98,27 @@ public:
    */
   void Mark();
 
+  /*
+   * Get the style data for a style struct.  This is the most important
+   * member function of nsIStyleContext.  It fills in a const pointer
+   * to a style data struct that is appropriate for the style context's
+   * frame.  This struct may be shared with other contexts (either in
+   * the rule tree or the style context tree), so it should not be
+   * modified.
+   *
+   * This function will NOT return null (even when out of memory) when
+   * given a valid style struct ID, so the result does not need to be
+   * null-checked.
+   *
+   * The typesafe global helper function |GetStyleData| (below) is
+   * preferred to the use of this function (and is a simple typesafe
+   * wrapper for this function).
+   *
+   * See also |nsIFrame::GetStyleData| and the other global
+   * |GetStyleData| in nsIFrame.h.
+   */
   const nsStyleStruct* GetStyleData(nsStyleStructID aSID);
+
   const nsStyleStruct* PeekStyleData(nsStyleStructID aSID);
 
   nsStyleStruct* GetUniqueStyleData(nsIPresContext* aPresContext, const nsStyleStructID& aSID);
diff --git a/layout/style/nsStyleSet.cpp b/layout/style/nsStyleSet.cpp
index e2a2aee206e..606c4474433 100644
--- a/layout/style/nsStyleSet.cpp
+++ b/layout/style/nsStyleSet.cpp
@@ -189,6 +189,10 @@ public:
   virtual nsresult BeginRuleTreeReconstruct();
   virtual nsresult EndRuleTreeReconstruct();
   
+  // For getting the cached default data in case we hit out-of-memory.
+  // To be used only by nsRuleNode.
+  virtual nsCachedStyleData* GetDefaultStyleData();
+
   virtual nsresult GetRuleTree(nsRuleNode** aResult);
   virtual nsresult ClearCachedDataInRuleTree(nsIStyleRule* aRule);
   
@@ -319,6 +323,9 @@ protected:
   
   void EnsureRuleWalker(nsIPresContext* aPresContext);
 
+  // Returns false on out-of-memory.
+  PRBool BuildDefaultStyleData(nsIPresContext* aPresContext);
+
   void ClearRuleProcessors(void);
   void ClearAgentRuleProcessors(void);
   void ClearUserRuleProcessors(void);
@@ -365,6 +372,11 @@ protected:
 
   nsCOMPtr<nsIStyleRuleSupplier> mStyleRuleSupplier; 
 
+  // To be used only in case of emergency, such as being out of memory
+  // or operating on a deleted rule node.  The latter should never
+  // happen, of course.
+  nsCachedStyleData mDefaultStyleData;
+
   nsRuleNode* mRuleTree; // This is the root of our rule tree.  It is a lexicographic tree of
                          // matched rules that style contexts use to look up properties.
   nsRuleNode* mOldRuleTree; // Used during rule tree reconstruction.
@@ -1143,25 +1155,55 @@ StyleSetImpl::WalkRuleProcessors(nsISupportsArrayEnumFunc aFunc,
     mOverrideRuleProcessors->EnumerateForwards(aFunc, aData);
 }
 
-#ifdef NS_DEBUG
-#define NS_ASSERT_REFCOUNT(ptr,cnt,msg) { \
-  nsrefcnt  count = ptr->AddRef();        \
-  ptr->Release();                         \
-  NS_ASSERTION(--count == cnt, msg);      \
-}
-#else
-#define NS_ASSERT_REFCOUNT(ptr,cnt,msg) {}
-#endif
-
 void StyleSetImpl::EnsureRuleWalker(nsIPresContext* aPresContext)
-{ 
+{
   if (mRuleWalker)
     return;
 
-  nsRuleNode::CreateRootNode(aPresContext, &mRuleTree);
+  if (!mDefaultStyleData.mResetData && !BuildDefaultStyleData(aPresContext)) {
+    mDefaultStyleData.Destroy(0, aPresContext);
+    return;
+  }
+
+  mRuleTree = nsRuleNode::CreateRootNode(aPresContext);
+  if (!mRuleTree)
+    return;
   mRuleWalker = new nsRuleWalker(mRuleTree);
 }
 
+PRBool StyleSetImpl::BuildDefaultStyleData(nsIPresContext* aPresContext)
+{
+  NS_ASSERTION(!mDefaultStyleData.mResetData &&
+               !mDefaultStyleData.mInheritedData,
+               "leaking default style data");
+  mDefaultStyleData.mResetData = new (aPresContext) nsResetStyleData;
+  if (!mDefaultStyleData.mResetData)
+    return PR_FALSE;
+  mDefaultStyleData.mInheritedData = new (aPresContext) nsInheritedStyleData;
+  if (!mDefaultStyleData.mInheritedData)
+    return PR_FALSE;
+
+#define SSARG_PRESCONTEXT aPresContext
+
+#define CREATE_DATA(name, type, args) \
+  if (!(mDefaultStyleData.m##type##Data->m##name##Data = \
+          new (aPresContext) nsStyle##name args)) \
+    return PR_FALSE;
+
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
+  CREATE_DATA(name, Inherited, ctor_args)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
+  CREATE_DATA(name, Reset, ctor_args)
+
+#include "nsStyleStructList.h"
+
+#undef STYLE_STRUCT_INHERITED
+#undef STYLE_STRUCT_RESET
+#undef SSARG_PRESCONTEXT
+
+  return PR_TRUE;
+}
+
 already_AddRefed<nsStyleContext>
 StyleSetImpl::ResolveStyleFor(nsIPresContext* aPresContext,
                               nsIContent* aContent,
@@ -1184,6 +1226,7 @@ StyleSetImpl::ResolveStyleFor(nsIPresContext* aPresContext,
         mDocRuleProcessors   ||
         mOverrideRuleProcessors) {
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       nsCOMPtr<nsIAtom> medium;
       aPresContext->GetMedium(getter_AddRefs(medium));
       RulesMatchingData data(aPresContext, medium, aContent, mRuleWalker);
@@ -1218,6 +1261,7 @@ StyleSetImpl::ResolveStyleForNonElement(nsIPresContext* aPresContext,
         mDocRuleProcessors   ||
         mOverrideRuleProcessors) {
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       result = GetContext(aPresContext, aParentContext,
                           nsCSSAnonBoxes::mozNonElement).get();
       NS_ASSERTION(mRuleWalker->AtRoot(), "rule walker must be at root");
@@ -1282,6 +1326,7 @@ StyleSetImpl::ResolvePseudoStyleFor(nsIPresContext* aPresContext,
       nsCOMPtr<nsIAtom> medium;
       aPresContext->GetMedium(getter_AddRefs(medium));
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       PseudoRulesMatchingData data(aPresContext, medium, aParentContent, 
                                    aPseudoTag, aComparator, mRuleWalker);
       FileRules(EnumPseudoRulesMatching, &data);
@@ -1324,6 +1369,7 @@ StyleSetImpl::ProbePseudoStyleFor(nsIPresContext* aPresContext,
       nsCOMPtr<nsIAtom> medium;
       aPresContext->GetMedium(getter_AddRefs(medium));
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       PseudoRulesMatchingData data(aPresContext, medium, aParentContent, 
                                    aPseudoTag, nsnull, mRuleWalker);
       FileRules(EnumPseudoRulesMatching, &data);
@@ -1378,11 +1424,15 @@ NS_IMETHODIMP
 StyleSetImpl::Shutdown(nsIPresContext* aPresContext)
 {
   delete mRuleWalker;
+  mRuleWalker = nsnull;
   if (mRuleTree)
   {
     mRuleTree->Destroy();
     mRuleTree = nsnull;
   }
+
+  mDefaultStyleData.Destroy(0, aPresContext);
+
   return NS_OK;
 }
 
@@ -1450,6 +1500,12 @@ StyleSetImpl::EndRuleTreeReconstruct()
   return NS_OK;
 }
 
+nsCachedStyleData*
+StyleSetImpl::GetDefaultStyleData()
+{
+  return &mDefaultStyleData;
+}
+
 nsresult
 StyleSetImpl::ClearCachedDataInRuleTree(nsIStyleRule* aInlineStyleRule)
 {
@@ -1507,6 +1563,7 @@ StyleSetImpl::ReParentStyleContext(nsIPresContext* aPresContext,
       nsRuleNode* ruleNode;
       aStyleContext->GetRuleNode(&ruleNode);
       EnsureRuleWalker(aPresContext);
+      NS_ENSURE_TRUE(mRuleWalker, nsnull);
       mRuleWalker->SetCurrentNode(ruleNode);
 
       already_AddRefed<nsStyleContext> result =
@@ -1845,14 +1902,9 @@ void StyleSetImpl::ListContexts(nsIFrame* aRootFrame, FILE* out, PRInt32 aIndent
 nsresult
 NS_NewStyleSet(nsIStyleSet** aInstancePtrResult)
 {
-  if (!aInstancePtrResult) {
-    return NS_ERROR_NULL_POINTER;
-  }
-
-  StyleSetImpl  *it = new StyleSetImpl();
-  if (!it) {
+  StyleSetImpl *it = new StyleSetImpl();
+  if (!it)
     return NS_ERROR_OUT_OF_MEMORY;
-  }
 
   return CallQueryInterface(it, aInstancePtrResult);
 }
diff --git a/layout/style/nsStyleStruct.cpp b/layout/style/nsStyleStruct.cpp
index 2ab1fa3fc69..83f06dbdac1 100644
--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -42,6 +42,7 @@
 #include "nsString.h"
 #include "nsUnitConversion.h"
 #include "nsIPresContext.h"
+#include "nsIDeviceContext.h"
 #include "nsIStyleRule.h"
 #include "nsISupportsArray.h"
 #include "nsCRT.h"
@@ -230,6 +231,17 @@ nsStyleFont::nsStyleFont(const nsStyleFont& aSrc)
 {
 }
 
+
+nsStyleFont::nsStyleFont(nsIPresContext* aPresContext)
+  : mFlags(NS_STYLE_FONT_DEFAULT)
+{
+  const nsFont* defaultFont;
+  aPresContext->GetDefaultFont(kPresContext_DefaultVariableFont_ID,
+                               &defaultFont);
+  mFont = *defaultFont;
+  mSize = mFont.size = nsStyleFont::ZoomText(aPresContext, mFont.size);
+}
+
 void* 
 nsStyleFont::operator new(size_t sz, nsIPresContext* aContext) CPP_THROW_NEW {
   void* result = nsnull;
@@ -253,6 +265,28 @@ nsChangeHint nsStyleFont::CalcDifference(const nsStyleFont& aOther) const
   return NS_STYLE_HINT_REFLOW;
 }
 
+inline float
+TextZoomFor(nsIPresContext* aPresContext)
+{
+  nsCOMPtr<nsIDeviceContext> dc;
+  aPresContext->GetDeviceContext(getter_AddRefs(dc));
+  float textZoom;
+  dc->GetTextZoom(textZoom);
+  return textZoom;
+}
+
+/* static */ nscoord
+nsStyleFont::ZoomText(nsIPresContext *aPresContext, nscoord aSize)
+{
+  return nscoord(float(aSize) * TextZoomFor(aPresContext));
+}
+
+/* static */ nscoord
+nsStyleFont::UnZoomText(nsIPresContext *aPresContext, nscoord aSize)
+{
+  return nscoord(float(aSize) / TextZoomFor(aPresContext));
+}
+
 nsChangeHint nsStyleFont::CalcFontDifference(const nsFont& aFont1, const nsFont& aFont2)
 {
   if ((aFont1.size == aFont2.size) && 
@@ -1004,6 +1038,8 @@ nsChangeHint nsStyleBackground::CalcDifference(const nsStyleBackground& aOther)
     && ((NS_STYLE_BG_ATTACHMENT_FIXED == mBackgroundAttachment) ||
         (NS_STYLE_BG_ATTACHMENT_FIXED == aOther.mBackgroundAttachment)))
     // this might require creation of a view
+    // XXX This probably doesn't call ApplyRenderingChangeToTree, which
+    // means we might not invalidate the canvas if this is the body.
     return NS_STYLE_HINT_FRAMECHANGE;
 
   if ((mBackgroundAttachment == aOther.mBackgroundAttachment) &&
diff --git a/layout/style/nsStyleStruct.h b/layout/style/nsStyleStruct.h
index 7af7e4a4456..11111feaa75 100644
--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -64,7 +64,7 @@ enum nsStyleStructID {
  * increase by 1.
  */
 
-#define STYLE_STRUCT(name, checkdata_cb) eStyleStruct_##name,
+#define STYLE_STRUCT(name, checkdata_cb, ctor_args) eStyleStruct_##name,
 #include "nsStyleStructList.h"
 #undef STYLE_STRUCT
 
@@ -96,12 +96,18 @@ struct nsStyleStruct {
 
 struct nsStyleFont : public nsStyleStruct {
   nsStyleFont(void);
+  nsStyleFont(const nsFont& aFont);
+  nsStyleFont(const nsStyleFont& aStyleFont);
+  nsStyleFont(nsIPresContext *aPresContext);
   ~nsStyleFont(void) {};
 
   NS_DEFINE_STATIC_STYLESTRUCTID_ACCESSOR(eStyleStruct_Font)
 
   nsChangeHint CalcDifference(const nsStyleFont& aOther) const;
   static nsChangeHint CalcFontDifference(const nsFont& aFont1, const nsFont& aFont2);
+
+  static nscoord ZoomText(nsIPresContext* aPresContext, nscoord aSize);
+  static nscoord UnZoomText(nsIPresContext* aPresContext, nscoord aSize);
   
   void* operator new(size_t sz, nsIPresContext* aContext) CPP_THROW_NEW;
   void Destroy(nsIPresContext* aContext);
@@ -112,10 +118,6 @@ struct nsStyleFont : public nsStyleStruct {
                         // which is our "actual size" and is enforced to be >= the user's
                         // preferred min-size. mFont.size should be used for display purposes
                         // while mSize is the value to return in getComputedStyle() for example.
-
-  nsStyleFont(const nsFont& aFont);
-  nsStyleFont(const nsStyleFont& aStyleFont);
-  nsStyleFont(nsIPresContext* aPresContext);
 };
 
 struct nsStyleColor : public nsStyleStruct {
diff --git a/layout/style/nsStyleStructList.h b/layout/style/nsStyleStructList.h
index f57734d1099..a16ab996ee2 100644
--- a/layout/style/nsStyleStructList.h
+++ b/layout/style/nsStyleStructList.h
@@ -44,40 +44,41 @@
  */
 
 #ifndef STYLE_STRUCT_INHERITED
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
-  STYLE_STRUCT(name, checkdata_cb)
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
+  STYLE_STRUCT(name, checkdata_cb, ctor_args)
 #define UNDEF_STYLE_STRUCT_INHERITED
 #endif
 
 #ifndef STYLE_STRUCT_RESET
-#define STYLE_STRUCT_RESET(name, checkdata_cb) STYLE_STRUCT(name, checkdata_cb)
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
+  STYLE_STRUCT(name, checkdata_cb, ctor_args)
 #define UNDEF_STYLE_STRUCT_RESET
 #endif
 
-STYLE_STRUCT_INHERITED(Font, CheckFontCallback)
-STYLE_STRUCT_INHERITED(Color, nsnull)
-STYLE_STRUCT_RESET(Background, nsnull)
-STYLE_STRUCT_INHERITED(List, nsnull)
-STYLE_STRUCT_RESET(Position, nsnull)
-STYLE_STRUCT_INHERITED(Text, nsnull)
-STYLE_STRUCT_RESET(TextReset, nsnull)
-STYLE_STRUCT_RESET(Display, nsnull)
-STYLE_STRUCT_INHERITED(Visibility, nsnull)
-STYLE_STRUCT_RESET(Content, nsnull)
-STYLE_STRUCT_INHERITED(Quotes, nsnull)
-STYLE_STRUCT_INHERITED(UserInterface, nsnull)
-STYLE_STRUCT_RESET(UIReset, nsnull)
-STYLE_STRUCT_RESET(Table, nsnull)
-STYLE_STRUCT_INHERITED(TableBorder, nsnull)
-STYLE_STRUCT_RESET(Margin, nsnull)
-STYLE_STRUCT_RESET(Padding, nsnull)
-STYLE_STRUCT_RESET(Border, nsnull)
-STYLE_STRUCT_RESET(Outline, nsnull)
+STYLE_STRUCT_INHERITED(Font, CheckFontCallback, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_INHERITED(Color, nsnull, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_RESET(Background, nsnull, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_INHERITED(List, nsnull, ())
+STYLE_STRUCT_RESET(Position, nsnull, ())
+STYLE_STRUCT_INHERITED(Text, nsnull, ())
+STYLE_STRUCT_RESET(TextReset, nsnull, ())
+STYLE_STRUCT_RESET(Display, nsnull, ())
+STYLE_STRUCT_INHERITED(Visibility, nsnull, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_RESET(Content, nsnull, ())
+STYLE_STRUCT_INHERITED(Quotes, nsnull, ())
+STYLE_STRUCT_INHERITED(UserInterface, nsnull, ())
+STYLE_STRUCT_RESET(UIReset, nsnull, ())
+STYLE_STRUCT_RESET(Table, nsnull, ())
+STYLE_STRUCT_INHERITED(TableBorder, nsnull, (SSARG_PRESCONTEXT))
+STYLE_STRUCT_RESET(Margin, nsnull, ())
+STYLE_STRUCT_RESET(Padding, nsnull, ())
+STYLE_STRUCT_RESET(Border, nsnull, ())
+STYLE_STRUCT_RESET(Outline, nsnull, (SSARG_PRESCONTEXT))
 #ifdef INCLUDE_XUL
-STYLE_STRUCT_RESET(XUL, nsnull)
+STYLE_STRUCT_RESET(XUL, nsnull, ())
 #endif
 #ifdef MOZ_SVG
-STYLE_STRUCT_INHERITED(SVG, nsnull)
+STYLE_STRUCT_INHERITED(SVG, nsnull, ())
 #endif
 
 #ifdef UNDEF_STYLE_STRUCT_INHERITED
diff --git a/layout/style/nsStyleUtil.cpp b/layout/style/nsStyleUtil.cpp
index 08ab6fcd701..4b16eee665b 100644
--- a/layout/style/nsStyleUtil.cpp
+++ b/layout/style/nsStyleUtil.cpp
@@ -66,11 +66,11 @@
 nsCachedStyleData::StyleStructInfo
 nsCachedStyleData::gInfo[] = {
 
-#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \
+#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
   { offsetof(nsCachedStyleData, mInheritedData), \
     offsetof(nsInheritedStyleData, m##name##Data), \
     PR_FALSE },
-#define STYLE_STRUCT_RESET(name, checkdata_cb) \
+#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
   { offsetof(nsCachedStyleData, mResetData), \
     offsetof(nsResetStyleData, m##name##Data), \
     PR_TRUE },