diff --git a/browser/base/content/browser-init.js b/browser/base/content/browser-init.js
index bee5309c04..d7fa2af364 100644
--- a/browser/base/content/browser-init.js
+++ b/browser/base/content/browser-init.js
@@ -72,7 +72,7 @@ var gBrowserInit = {
     updateBookmarkToolbarVisibility();
 
     // Set a sane starting width/height for all resolutions on new profiles.
-    if (ChromeUtils.shouldResistFingerprinting("RoundWindowSize", null)) {
+    if (true || ChromeUtils.shouldResistFingerprinting("RoundWindowSize", null)) {
       // When the fingerprinting resistance is enabled, making sure that we don't
       // have a maximum window to interfere with generating rounded window dimensions.
       document.documentElement.setAttribute("sizemode", "normal");
@@ -302,6 +302,48 @@ var gBrowserInit = {
       )?.removeAttribute("key");
     }
 
+    // Set default size
+    window.resizeTo(1280, 1040);
+
+    // Hijack the outer window size
+    let outerWidth, outerHeight;
+    if ((outerWidth = ChromeUtils.camouGetInt("window.outerWidth"))) {
+      document.documentElement.style.setProperty('width', outerWidth + 'px');
+      browser.style.setProperty('width', outerWidth + 'px');
+      window.resizeTo(outerWidth, window.outerHeight);
+    }
+    if ((outerHeight = ChromeUtils.camouGetInt("window.outerHeight"))) {
+      document.documentElement.style.setProperty('height', outerHeight + 'px');
+      browser.style.setProperty('height', outerHeight + 'px');
+      window.resizeTo(window.outerWidth, outerHeight);
+    }
+    browser.style.setProperty('box-sizing', 'content-box');
+
+    // Hijack the inner window size
+    let innerWidth = ChromeUtils.camouGetInt("window.innerWidth") || ChromeUtils.camouGetInt("document.body.clientWidth");
+    let innerHeight = ChromeUtils.camouGetInt("window.innerHeight") || ChromeUtils.camouGetInt("document.body.clientHeight");
+
+    if (innerWidth || innerHeight) {
+      let win_inner_style = document.createElement('style');
+      win_inner_style.innerHTML = `
+        .browserStack {
+          ${innerWidth ? `width: ${innerWidth}px !important;` : ''}
+          ${innerHeight ? `height: ${innerHeight}px !important;` : ''}
+          ${innerHeight ? `flex: unset !important;` : ''}
+          overflow: auto;
+          contain: size;
+          scrollbar-width: none;
+        }
+      `;
+      document.head.appendChild(win_inner_style);
+    }
+
+    if (innerWidth && innerHeight && !(outerWidth || outerHeight)) {
+      let stackRect = __browserStack.getBoundingClientRect();
+      let toolbarTop = stackRect.y;
+      window.resizeBy(width - innerWidth, height + toolbarTop - innerHeight);
+    }
+
     this._loadHandled = true;
   },