diff --git a/widget/gtk/nsLookAndFeel.h b/widget/gtk/nsLookAndFeel.h
--- a/widget/gtk/nsLookAndFeel.h
+++ b/widget/gtk/nsLookAndFeel.h
@@ -76,13 +76,14 @@ protected:
     nscolor sTextSelectedBackground;
     nscolor sMozScrollbar;
 #if (MOZ_WIDGET_GTK == 3)
     nscolor sInfoBarText;
 #endif
     char16_t sInvisibleCharacter;
     float   sCaretRatio;
     bool    sMenuSupportsDrag;
+    bool    mInitialized;
 
-    void Init();
+    void EnsureInit();
 };
 
 #endif

diff --git a/widget/gtk/nsLookAndFeel.cpp b/widget/gtk/nsLookAndFeel.cpp
--- a/widget/gtk/nsLookAndFeel.cpp
+++ b/widget/gtk/nsLookAndFeel.cpp
@@ -45,19 +45,19 @@ using mozilla::LookAndFeel;
                        (int)((c).blue*255), (int)((c).alpha*255)))
 
 nsLookAndFeel::nsLookAndFeel()
     : nsXPLookAndFeel(),
 #if (MOZ_WIDGET_GTK == 2)
       mStyle(nullptr),
 #endif
       mDefaultFontCached(false), mButtonFontCached(false),
-      mFieldFontCached(false), mMenuFontCached(false)
+      mFieldFontCached(false), mMenuFontCached(false),
+      mInitialized(false)
 {
-    Init();    
 }
 
 nsLookAndFeel::~nsLookAndFeel()
 {
 #if (MOZ_WIDGET_GTK == 2)
     g_object_unref(mStyle);
 #endif
 }
@@ -219,16 +219,18 @@ GetBorderColors(GtkStyleContext* aContex
     *aDarkColor = GDK_RGBA_TO_NS_RGBA(darkColor);
     return ret;
 }
 #endif
 
 nsresult
 nsLookAndFeel::NativeGetColor(ColorID aID, nscolor& aColor)
 {
+    EnsureInit();
+
 #if (MOZ_WIDGET_GTK == 3)
     GdkRGBA gdk_color;
 #endif
     nsresult res = NS_OK;
 
     switch (aID) {
         // These colors don't seem to be used for anything anymore in Mozilla
         // (except here at least TextSelectBackground and TextSelectForeground)
@@ -670,16 +672,21 @@ nsLookAndFeel::GetIntImpl(IntID aID, int
         break;
     }
 
     res = nsXPLookAndFeel::GetIntImpl(aID, aResult);
     if (NS_SUCCEEDED(res))
         return res;
     res = NS_OK;
 
+    // We use delayed initialization by EnsureInit() here
+    // to make sure mozilla::Preferences is available (Bug 115807).
+    // eIntID_UseAccessibilityTheme is requested before user preferences
+    // are read, and so EnsureInit(), which depends on preference values,
+    // is deliberately delayed until required.
     switch (aID) {
     case eIntID_CaretBlinkTime:
         {
             GtkSettings *settings;
             gint blink_time;
             gboolean blink;
 
             settings = gtk_settings_get_default ();
@@ -832,16 +839,17 @@ nsLookAndFeel::GetIntImpl(IntID aID, int
     case eIntID_IMESelectedRawTextUnderlineStyle:
     case eIntID_IMESelectedConvertedTextUnderline:
         aResult = NS_STYLE_TEXT_DECORATION_STYLE_NONE;
         break;
     case eIntID_SpellCheckerUnderlineStyle:
         aResult = NS_STYLE_TEXT_DECORATION_STYLE_WAVY;
         break;
     case eIntID_MenuBarDrag:
+        EnsureInit();
         aResult = sMenuSupportsDrag;
         break;
     case eIntID_ScrollbarButtonAutoRepeatBehavior:
         aResult = 1;
         break;
     case eIntID_SwipeAnimationEnabled:
         aResult = 0;
         break;
@@ -872,16 +880,17 @@ nsLookAndFeel::GetFloatImpl(FloatID aID,
     switch (aID) {
     case eFloatID_IMEUnderlineRelativeSize:
         aResult = 1.0f;
         break;
     case eFloatID_SpellCheckerUnderlineRelativeSize:
         aResult = 1.0f;
         break;
     case eFloatID_CaretAspectRatio:
+        EnsureInit();
         aResult = sCaretRatio;
         break;
     default:
         aResult = -1.0;
         res = NS_ERROR_FAILURE;
     }
     return res;
 }
@@ -1052,21 +1061,25 @@ nsLookAndFeel::GetFontImpl(FontID aID, n
   }
 
   aFontName = *cachedFontName;
   aFontStyle = *cachedFontStyle;
   return true;
 }
 
 void
-nsLookAndFeel::Init()
+nsLookAndFeel::EnsureInit()
 {
     GdkColor colorValue;
     GdkColor *colorValuePtr;
 
+    if (mInitialized)
+        return;
+    mInitialized = true;
+
 #if (MOZ_WIDGET_GTK == 2)
     NS_ASSERTION(!mStyle, "already initialized");
     // GtkInvisibles come with a refcount that is not floating
     // (since their initialization code calls g_object_ref_sink) and
     // their destroy code releases that reference (which means they
     // have to be explicitly destroyed, since calling unref enough
     // to cause destruction would lead to *another* unref).
     // However, this combination means that it's actually still ok
@@ -1445,16 +1458,17 @@ nsLookAndFeel::Init()
 
     gtk_widget_destroy(window);
 }
 
 // virtual
 char16_t
 nsLookAndFeel::GetPasswordCharacterImpl()
 {
+    EnsureInit();
     return sInvisibleCharacter;
 }
 
 void
 nsLookAndFeel::RefreshImpl()
 {
     nsXPLookAndFeel::RefreshImpl();
 
@@ -1463,15 +1477,15 @@ nsLookAndFeel::RefreshImpl()
     mFieldFontCached = false;
     mMenuFontCached = false;
 
 #if (MOZ_WIDGET_GTK == 2)
     g_object_unref(mStyle);
     mStyle = nullptr;
 #endif
 
-    Init();
+    mInitialized = false;
 }
 
 bool
 nsLookAndFeel::GetEchoPasswordImpl() {
     return false;
 }