chore: Avoid EINVAL in fake-firefox-binary (mozilla#3451)

Author: Rob--W

tests/functional/common.js

@@ -21,19 +21,18 @@ export const webExt = process.env.TEST_WEB_EXT_BIN
 export const fixturesDir = path.join(functionalTestsDir, '..', 'fixtures');
 export const minimalAddonPath = path.join(fixturesDir, 'minimal-web-ext');
 export const fixturesUseAsLibrary = path.join(fixturesDir, 'webext-as-library');
+// NOTE: Depends on preload_on_windows.cjs to load this on Windows!
 export const fakeFirefoxPath = path.join(
   functionalTestsDir,
-  process.platform === 'win32'
-    ? 'fake-firefox-binary.bat'
-    : 'fake-firefox-binary.js',
+  'fake-firefox-binary.js',
 );
 export const fakeServerPath = path.join(
   functionalTestsDir,
   'fake-amo-server.js',
 );
 
 export const chromeExtPath = path.join(fixturesDir, 'chrome-extension-mv3');
-// NOTE: Depends on preload_on_windows.cjs to load this!
+// NOTE: Depends on preload_on_windows.cjs to load this on Windows!
 export const fakeChromePath = path.join(
   functionalTestsDir,
   'fake-chrome-binary.js',

tests/functional/fake-firefox-binary.bat

@@ -20,7 +20,10 @@ const child_process = require('node:child_process');
 const orig_spawn = child_process.spawn;
 child_process.spawn = function(command, args, options, ...remainingArgs) {
   if (typeof command === 'string') {
-    if (command.endsWith('fake-chrome-binary.js')) {
+    if (
+      command.endsWith('fake-chrome-binary.js') ||
+      command.endsWith('fake-firefox-binary.js')
+    ) {
       args = args ? [command, ...args] : [command];
       command = process.execPath;
     }