ci: fix firefox --version check (stdout match, not exit code)

firefox.exe --version on Windows prints the version string but may
return non-zero exit code (sub-process fork quirk). The previous check
treated that as a launch failure, producing a false-positive failure
across the whole matrix while the binary actually launched cleanly.

Switch to matching the printed output instead, so we only fail when the
binary really can't start.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/firefox-launch-matrix.yml

@@ -71,11 +71,15 @@ jobs:
               exit 1
           }
           Write-Host "Launching: $ffPath --version"
-          & $ffPath --version
-          if ($LASTEXITCODE -ne 0) {
-              Write-Error "firefox.exe --version returned $LASTEXITCODE"
-              exit $LASTEXITCODE
+          # NOTE: firefox.exe --version on Windows prints the version but may
+          # return non-zero exit code (sub-process fork quirk). Check stdout.
+          $output = & $ffPath --version 2>&1 | Out-String
+          Write-Host "Output: $output"
+          if ($output -notmatch 'Mozilla Firefox \d') {
+              Write-Error "firefox.exe --version did not print a Mozilla Firefox version. Output was: $output"
+              exit 1
           }
+          Write-Host "OK: firefox.exe runs and prints version."
 
       - name: Run reporter's exact InvisiblePlaywright snippet
         run: |