message: It might be wct-browser-legacy/browser.js that indicates you're doing wct, not just web-component-tester/browser.js
diff: @@ -167,7 +167,9 @@ function compileHtml(
  const src = dom5.getAttribute(scriptTag, 'src');
  const isInline = !src;
  - if (src && src.includes('web-component-tester/browser.js')) {
  + if (src &&
  + (src.includes('web-component-tester/browser.js') ||
  + src.includes('wct-browser-legacy/browser.js'))) {
  wctScriptTag = scriptTag;
  }
  