diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
index ea952f125716..0dab1645cff6 100644
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -1014,7 +1014,7 @@ CanvasRenderingContext2D::ParseColor(const nsAString& aString,
     *aColor = value.GetColorValue();
   } else {
     // otherwise resolve it
-    nsIPresShell* presShell = GetPresShell();
+    nsCOMPtr<nsIPresShell> presShell = GetPresShell();
     nsRefPtr<nsStyleContext> parentContext;
     if (mCanvasElement && mCanvasElement->IsInDoc()) {
       // Inherit from the canvas element.
@@ -2151,9 +2151,15 @@ GetFontParentStyleContext(Element* aElement, nsIPresShell* presShell,
                           ErrorResult& error)
 {
   if (aElement && aElement->IsInDoc()) {
-    // inherit from the canvas element
-    return nsComputedDOMStyle::GetStyleContextForElement(aElement, nullptr,
-                                                         presShell);
+    // Inherit from the canvas element.
+    nsRefPtr<nsStyleContext> result =
+      nsComputedDOMStyle::GetStyleContextForElement(aElement, nullptr,
+                                                    presShell);
+    if (!result) {
+      error.Throw(NS_ERROR_FAILURE);
+      return nullptr;
+    }
+    return result.forget();
   }
 
   // otherwise inherit from default (10px sans-serif)
@@ -2168,7 +2174,14 @@ GetFontParentStyleContext(Element* aElement, nsIPresShell* presShell,
 
   nsTArray<nsCOMPtr<nsIStyleRule>> parentRules;
   parentRules.AppendElement(parentRule);
-  return presShell->StyleSet()->ResolveStyleForRules(nullptr, parentRules);
+  nsRefPtr<nsStyleContext> result =
+    presShell->StyleSet()->ResolveStyleForRules(nullptr, parentRules);
+
+  if (!result) {
+    error.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+  return result.forget();
 }
 
 static bool
@@ -2222,6 +2235,12 @@ GetFontStyleContext(Element* aElement, const nsAString& aFont,
     return nullptr;
   }
 
+  MOZ_RELEASE_ASSERT(parentContext,
+                     "GetFontParentStyleContext should have returned an error if it couldn't get a parent context.");
+
+  MOZ_ASSERT(!presShell->IsDestroying(),
+             "GetFontParentStyleContext should have returned an error if the presshell is being destroyed.");
+
   nsTArray<nsCOMPtr<nsIStyleRule>> rules;
   rules.AppendElement(rule);
   // add a rule to prevent text zoom from affecting the style
@@ -2299,7 +2318,7 @@ CanvasRenderingContext2D::ParseFilter(const nsAString& aString,
     return false;
   }
 
-  nsIPresShell* presShell = GetPresShell();
+  nsCOMPtr<nsIPresShell> presShell = GetPresShell();
   if (!presShell) {
     error.Throw(NS_ERROR_FAILURE);
     return false;
@@ -3034,6 +3053,13 @@ CanvasRenderingContext2D::TransformWillUpdate()
 void
 CanvasRenderingContext2D::SetFont(const nsAString& font,
                                   ErrorResult& error)
+{
+  SetFontInternal(font, error);
+}
+
+bool
+CanvasRenderingContext2D::SetFontInternal(const nsAString& font,
+                                          ErrorResult& error)
 {
   /*
     * If font is defined with relative units (e.g. ems) and the parent
@@ -3046,20 +3072,20 @@ CanvasRenderingContext2D::SetFont(const nsAString& font,
   if (!mCanvasElement && !mDocShell) {
     NS_WARNING("Canvas element must be non-null or a docshell must be provided");
     error.Throw(NS_ERROR_FAILURE);
-    return;
+    return false;
   }
 
-  nsIPresShell* presShell = GetPresShell();
+  nsCOMPtr<nsIPresShell> presShell = GetPresShell();
   if (!presShell) {
     error.Throw(NS_ERROR_FAILURE);
-    return;
+    return false;
   }
 
   nsString usedFont;
   nsRefPtr<nsStyleContext> sc =
     GetFontStyleContext(mCanvasElement, font, presShell, usedFont, error);
   if (!sc) {
-    return;
+    return false;
   }
 
   const nsStyleFont* fontStyle = sc->StyleFont();
@@ -3099,6 +3125,8 @@ CanvasRenderingContext2D::SetFont(const nsAString& font,
   CurrentState().fontFont.size = fontStyle->mSize;
   CurrentState().fontLanguage = fontStyle->mLanguage;
   CurrentState().fontExplicitLanguage = fontStyle->mExplicitLanguage;
+
+  return true;
 }
 
 void
@@ -3693,7 +3721,12 @@ CanvasRenderingContext2D::DrawOrMeasureText(const nsAString& aRawText,
   }
 
   gfxFontGroup* currentFontStyle = GetCurrentFontStyle();
-  NS_ASSERTION(currentFontStyle, "font group is null");
+  if (!currentFontStyle) {
+    return NS_ERROR_FAILURE;
+  }
+
+  MOZ_ASSERT(!presShell->IsDestroying(),
+             "GetCurrentFontStyle() should have returned null if the presshell is being destroyed");
 
   // ensure user font set is up to date
   currentFontStyle->
@@ -3891,8 +3924,9 @@ gfxFontGroup *CanvasRenderingContext2D::GetCurrentFontStyle()
     ErrorResult err;
     NS_NAMED_LITERAL_STRING(kDefaultFontStyle, "10px sans-serif");
     static float kDefaultFontSize = 10.0;
-    SetFont(kDefaultFontStyle, err);
-    if (err.Failed()) {
+    nsCOMPtr<nsIPresShell> presShell = GetPresShell();
+    bool fontUpdated = SetFontInternal(kDefaultFontStyle, err);
+    if (err.Failed() || !fontUpdated) {
       gfxFontStyle style;
       style.size = kDefaultFontSize;
       CurrentState().fontGroup =
@@ -3901,9 +3935,7 @@ gfxFontGroup *CanvasRenderingContext2D::GetCurrentFontStyle()
                                                     nullptr);
       if (CurrentState().fontGroup) {
         CurrentState().font = kDefaultFontStyle;
-
-        nsIPresShell* presShell = GetPresShell();
-        if (presShell) {
+        if (presShell && !presShell->IsDestroying()) {
           CurrentState().fontGroup->SetTextPerfMetrics(
             presShell->GetPresContext()->GetTextPerfMetrics());
         }
@@ -3911,7 +3943,6 @@ gfxFontGroup *CanvasRenderingContext2D::GetCurrentFontStyle()
         NS_ERROR("Default canvas font is invalid");
       }
     }
-
   }
 
   return CurrentState().fontGroup;
diff --git a/dom/canvas/CanvasRenderingContext2D.h b/dom/canvas/CanvasRenderingContext2D.h
index b14fc2cc195d..893d4ddf0355 100644
--- a/dom/canvas/CanvasRenderingContext2D.h
+++ b/dom/canvas/CanvasRenderingContext2D.h
@@ -597,6 +597,10 @@ protected:
                    nsTArray<nsStyleFilter>& aFilterChain,
                    ErrorResult& error);
 
+  // Returns whether the font was successfully updated.
+  bool SetFontInternal(const nsAString& font, mozilla::ErrorResult& error);
+
+
   /**
    * Creates the error target, if it doesn't exist
    */
@@ -631,7 +635,7 @@ protected:
    */
   RenderingMode EnsureTarget(RenderingMode aRenderMode = RenderingMode::DefaultBackendMode);
 
-  /*
+  /**
    * Disposes an old target and prepares to lazily create a new target.
    */
   void ClearTarget();
@@ -867,10 +871,10 @@ protected:
 protected:
   gfxFontGroup *GetCurrentFontStyle();
 
-  /*
-    * Implementation of the fillText, strokeText, and measure functions with
-    * the operation abstracted to a flag.
-    */
+  /**
+   * Implementation of the fillText, strokeText, and measure functions with
+   * the operation abstracted to a flag.
+   */
   nsresult DrawOrMeasureText(const nsAString& text,
                              float x,
                              float y,
diff --git a/dom/html/HTMLCanvasElement.cpp b/dom/html/HTMLCanvasElement.cpp
index 6e6e36ada435..214a53adae18 100644
--- a/dom/html/HTMLCanvasElement.cpp
+++ b/dom/html/HTMLCanvasElement.cpp
@@ -878,19 +878,21 @@ HTMLCanvasElement::UpdateContext(JSContext* aCx, JS::Handle<JS::Value> aNewConte
 
   nsIntSize sz = GetWidthHeight();
 
-  nsresult rv = mCurrentContext->SetIsOpaque(HasAttr(kNameSpaceID_None, nsGkAtoms::moz_opaque));
+  nsCOMPtr<nsICanvasRenderingContextInternal> currentContext = mCurrentContext;
+
+  nsresult rv = currentContext->SetIsOpaque(HasAttr(kNameSpaceID_None, nsGkAtoms::moz_opaque));
   if (NS_FAILED(rv)) {
     mCurrentContext = nullptr;
     return rv;
   }
 
-  rv = mCurrentContext->SetContextOptions(aCx, aNewContextOptions);
+  rv = currentContext->SetContextOptions(aCx, aNewContextOptions);
   if (NS_FAILED(rv)) {
     mCurrentContext = nullptr;
     return rv;
   }
 
-  rv = mCurrentContext->SetDimensions(sz.width, sz.height);
+  rv = currentContext->SetDimensions(sz.width, sz.height);
   if (NS_FAILED(rv)) {
     mCurrentContext = nullptr;
     return rv;