diff --git a/build/lib/chromiumRebaseL10n.js b/build/lib/chromiumRebaseL10n.js
index bc3e0a5b2c9f..20cf3ea56326 100644
--- a/build/lib/chromiumRebaseL10n.js
+++ b/build/lib/chromiumRebaseL10n.js
@@ -6,8 +6,8 @@ const config = require('../lib/config')
 const util = require('../lib/util')
 const {rebaseBraveStringFilesOnChromiumL10nFiles, braveAutoGeneratedPaths} = require('./l10nUtil')
 
-const chromiumRebaseL10n = (options) => {
-  rebaseBraveStringFilesOnChromiumL10nFiles()
+const chromiumRebaseL10n = async (options) => {
+  await rebaseBraveStringFilesOnChromiumL10nFiles()
   braveAutoGeneratedPaths.forEach((sourceStringPath) => {
     const cmdOptions = config.defaultOptions
     cmdOptions.cwd = config.projects['brave-core'].dir
diff --git a/build/lib/l10nUtil.js b/build/lib/l10nUtil.js
index 1448a4117570..5d77cdc686c6 100644
--- a/build/lib/l10nUtil.js
+++ b/build/lib/l10nUtil.js
@@ -104,18 +104,38 @@ module.exports.allBravePaths = module.exports.braveNonGeneratedPaths.concat(modu
 // This is because only 1 xtb is created per grd per locale even if it has multiple grdp files.
 module.exports.braveTopLevelPaths = module.exports.allBravePaths.filter((x) => ['grd', 'json'].includes(x.split('.').pop()))
 
+
 // This simply reads Chromium files that are passed to it and replaces branding strings
 // with Brave specific branding strings.
 // Do not use this for filtering XML, instead use chromium-rebase-l10n.py.
 // Only add idempotent replacements here (i.e. don't append replace A with AX here)
-module.exports.rebaseBraveStringFilesOnChromiumL10nFiles = (path) =>
-  Object.entries(chromiumToAutoGeneratedBraveMapping).forEach(([sourcePath, destPath]) =>
-    fs.writeFileSync(destPath,
-      fs.readFileSync(sourcePath, 'utf8')
-        .replace(/Automatically send usage statistics and crash reports to Google/g, 'Automatically send crash reports to Google')
-        .replace(/Automatically sends usage statistics and crash reports to Google/g, 'Automatically sends crash reports to Google')
-        .replace(/The Chromium Authors/g, 'Brave Software Inc')
-        .replace(/Google Chrome/g, 'Brave')
-        .replace(/Chromium/g, 'Brave')
-        .replace(/Chrome/g, 'Brave')
-        .replace(/Google/g, 'Brave'), 'utf8'))
+module.exports.rebaseBraveStringFilesOnChromiumL10nFiles = async function (path) {
+  const ops = Object.entries(chromiumToAutoGeneratedBraveMapping).map(async ([sourcePath, destPath]) => {
+    let contents = await new Promise(resolve => fs.readFile(sourcePath, 'utf8', (err, data) => resolve(data)))
+    for (const replacement of defaultReplacements) {
+      contents = contents.replace(replacement[0], replacement[1])
+    }
+    await new Promise(resolve => fs.writeFile(destPath, contents, 'utf8', resolve))
+  })
+  await Promise.all(ops)
+}
+
+// Straight-forward string replacement list.
+// Consider mapping chromium resource ID to a new brave resource ID
+// for whole-message replacements, instead of adding to this list.
+const defaultReplacements = [
+  [/Automatically send usage statistics and crash reports to Google/g, 'Automatically send crash reports to Google'],
+  [/Automatically sends usage statistics and crash reports to Google/g, 'Automatically sends crash reports to Google'],
+  [/The Chromium Authors/g, 'Brave Software Inc'],
+  [/Google Chrome/g, 'Brave'],
+  [/Chromium/g, 'Brave'],
+  [/Chrome/g, 'Brave'],
+  [/Google/g, 'Brave'],
+  [/You're incognito/g, 'This is a private window'],
+  [/an incognito/g, 'a private'],
+  [/an Incognito/g, 'a Private'],
+  [/incognito/g, 'private'],
+  [/Incognito/g, 'Private'],
+  [/inco\&amp\;gnito/g, '&private'],
+  [/Inco\&amp\;gnito/g, '&Private'],
+]