Backed out changeset 474012e38b60 (bug 1951690) as requested by developer.

xpfe/appshell/AppWindow.h

@@ -192,6 +192,7 @@ class AppWindow final : public nsIBaseWindow,
   NS_IMETHOD EnsurePrimaryContentTreeOwner();
   NS_IMETHOD EnsurePrompter();
   NS_IMETHOD EnsureAuthPrompter();
+  NS_IMETHOD ForceRoundedDimensions();
   NS_IMETHOD GetAvailScreenSize(int32_t* aAvailWidth, int32_t* aAvailHeight);
 
   void FinishFullscreenChange(bool aInFullscreen);

xpfe/appshell/nsAppShellService.cpp

@@ -166,19 +166,6 @@ nsAppShellService::CreateTopLevelWindow(nsIAppWindow* aParent, nsIURI* aUrl,
   if (NS_SUCCEEDED(rv)) {
     // the addref resulting from this is the owning addref for this window
     RegisterTopLevelWindow(*aResult);
-#ifdef XP_WIN
-    // On Windows, we sometimes use PreXULSkeletonUI to show a window early.
-    // However, it doesn't start with the right RFP'd size, so we rescale it.
-    if (nsContentUtils::ShouldResistFingerprinting(
-            "When RFP is enabled, we unconditionally round new window sizes. "
-            "The code paths that create new windows are complicated, and this "
-            "is a conservative behavior to avoid exempting something that "
-            "shouldn't be. It also presents a uniform behavior for something "
-            "that's very browser-related.",
-            RFPTarget::RoundWindowSize)) {
-      (*aResult)->ForceRoundedDimensions();
-    }
-#endif
   }
 
   return rv;

xpfe/appshell/nsIAppWindow.idl

@@ -97,11 +97,6 @@ interface nsIAppWindow : nsISupports
    */
   void showModal();
 
-  /**
-   * Rounds the window dimensions for fingerprinting resistance.
-   */
-  void forceRoundedDimensions();
-
   /**
    * Locks the aspect ratio for a window.
    * @param aShouldLock boolean