Potentially standardize window.find() #3539

See:

• https://www.chromestatus.com/metrics/feature/timeline/popularity/696 (currently 0.012% of page loads)
• https://bugzilla.mozilla.org/show_bug.cgi?id=672395
• https://bugs.webkit.org/show_bug.cgi?id=64761
• https://bugs.chromium.org/p/chromium/issues/detail?id=695564

Related #2858.