diff --git a/browser/base/content/browser-init.js b/browser/base/content/browser-init.js
index 1cfa4b8497..bdf8d7202e 100644
--- a/browser/base/content/browser-init.js
+++ b/browser/base/content/browser-init.js
@@ -3,6 +3,16 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+const { AddonManager } = ChromeUtils.importESModule(
+  "resource://gre/modules/AddonManager.sys.mjs",
+  { global: "shared" }
+);
+const { FileUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/FileUtils.sys.mjs",
+  { global: "contextual" }
+);
+
+
 let _resolveDelayedStartup;
 var delayedStartupPromise = new Promise(resolve => {
   _resolveDelayedStartup = resolve;
@@ -72,7 +82,7 @@ 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");
@@ -366,9 +417,152 @@ 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);
+    }
+
+    // Install addons if specified
+    let addonPaths = ChromeUtils.camouGetStringList("addons");
+    if (addonPaths?.length) {
+      Promise.all(addonPaths.map(path => this.installTemporaryAddon(path)))
+        .then(addons => ChromeUtils.camouDebug("Installed " + addons.length + " addon(s)"))
+        .catch(e => ChromeUtils.camouDebug("Failed to install addons: " + e));
+    }
+
+    // Certificate handling
+    let certsPaths = ChromeUtils.camouGetStringList("certificatePaths");
+    let certsRaw = ChromeUtils.camouGetStringList("certificates");
+    
+    if (certsPaths?.length || certsRaw?.length) {
+      ChromeUtils.camouDebug("Found certificates to import");
+      // Set up certificate database
+      var certdb = Cc["@mozilla.org/security/x509certdb;1"].getService(Ci.nsIX509CertDB);
+      var certdb2 = certdb;
+      try {
+        certdb2 = Cc["@mozilla.org/security/x509certdb;1"].getService(Ci.nsIX509CertDB2);
+      } catch (e) {}
+      
+      // Handle certificate files if any
+      if (certsPaths?.length) {
+        ChromeUtils.camouDebug("Processing " + certsPaths.length + " certificate files");
+        Promise.all(certsPaths.map(path => this.readCertFile(path)))
+          .then(certDataArray => {
+            // Import each certificate using map
+            certDataArray.map(certData => 
+              this.importCertificate(certdb2, certData, "from file")
+            );
+          })
+          .catch(e => ChromeUtils.camouDebug("Failed to read certificate files: " + e));
+      }
+      
+      // Handle raw certificate strings if any
+      if (certsRaw?.length) {
+        ChromeUtils.camouDebug("Processing " + certsRaw.length + " raw certificates");
+        // Process all raw certificates using map
+        certsRaw.map(rawCert => {
+          try {
+            let certData = this.processRawCertificate(rawCert);
+            ChromeUtils.camouDebug("Importing raw certificate: " + certData);
+            this.importCertificate(certdb2, certData, "raw");
+          } catch (e) {
+            ChromeUtils.camouDebug("Failed to process raw certificate: " + e);
+          }
+        });
+      }
+    }
+
     this._loadHandled = true;
   },
 
+  importCertificate(certdb, certData, source) {
+    try {
+      certdb.addCertFromBase64(certData, "C,C,C", "");
+      ChromeUtils.camouDebug("Successfully imported " + source + " certificate");
+    } catch (e) {
+      ChromeUtils.camouDebug("Failed to import " + source + " certificate: " + e);
+    }
+  },
+
+  processRawCertificate(content) {
+    // Process the certificate content (remove markers and newlines)
+    return content.replace(/\-{5}[\w]+\s[\w]+\-{5}/g, "").replace(/\s/g, "");
+  },
+
+  async readCertFile(path) {
+    try {
+      ChromeUtils.camouDebug("Reading certificate file: " + path);
+      const file = new FileUtils.File(path);
+      const ioService = Cc["@mozilla.org/network/io-service;1"].getService(Ci.nsIIOService);
+      const channel = ioService.newChannelFromURI(
+        ioService.newFileURI(file),
+        null,
+        Services.scriptSecurityManager.getSystemPrincipal(),
+        null,
+        Ci.nsILoadInfo.SEC_ALLOW_CROSS_ORIGIN_SEC_CONTEXT_IS_NULL,
+        Ci.nsIContentPolicy.TYPE_OTHER
+      );
+      
+      const inputStream = Cc["@mozilla.org/scriptableinputstream;1"]
+                           .createInstance(Ci.nsIScriptableInputStream);
+      const input = channel.open();
+      inputStream.init(input);
+      
+      let content = inputStream.read(input.available());
+      inputStream.close();
+      input.close();
+      
+      return this.processRawCertificate(content);
+    } catch (e) {
+      ChromeUtils.camouDebug("Error reading certificate file: " + e);
+      throw e;
+    }
+  },
+
+  async installTemporaryAddon(addonPath) {
+    const addonFile = new FileUtils.File(addonPath);
+    const addon = await AddonManager.installTemporaryAddon(addonFile);
+    Services.obs.notifyObservers(null, "devtools-installed-addon", addon.id);
+    return addon;
+  },
+
   _cancelDelayedStartup() {
     window.removeEventListener("MozAfterPaint", this._boundDelayedStartup);
     this._boundDelayedStartup = null;