diff --git a/src/browsers.js b/src/browsers.js
index 0598e37..22334de 100644
--- a/src/browsers.js
+++ b/src/browsers.js
@@ -127,15 +127,19 @@ const LocalBrowser = {
   }
 };
 
+// - iterate from a Set to de-duplicate because `PROGRAMFILES`, and `ProgramW6432` are
+//   often "C:\Program Files" which, we'd otherwise check three times.
+// - use filter() to remove empty entries.
+//
 // https://github.com/karma-runner/karma-chrome-launcher/blob/v3.2.0/index.js
 // https://github.com/vweevers/win-detect-browsers/blob/v7.0.0/lib/browsers.js
-const WINDOWS_DIRS = [
+const WINDOWS_DIRS = new Set([
   process.env.LOCALAPPDATA,
   process.env.PROGRAMFILES,
   process.env['PROGRAMFILES(X86)'],
   process.env.ProgramW6432,
   'C:\\Program Files'
-].filter(Boolean);
+].filter(Boolean));
 
 function createFirefoxPrefsJs (prefs) {
   let js = '';
@@ -259,6 +263,9 @@ async function firefox (url, signal, logger) {
 }
 
 async function chromium (paths, url, signal, logger) {
+  if (process.platform === 'win32') {
+    logger.debug('whatsinthere', [...WINDOWS_DIRS]);
+  }
   const dataDir = LocalBrowser.makeTempDir();
   // https://github.com/GoogleChrome/chrome-launcher/blob/main/docs/chrome-flags-for-tools.md
   const args = [