Is XSLT Polyfill safe?

This extension applies an XSLT polyfill to XML pages that include XSLT instructions.

It detects raw XML files with XML stylesheet processing instructions and transforms them into viewable HTML when needed. It also injects a polyfilled XSLTProcessor so JavaScript usage can continue when native browser support is unavailable. The description states that processing is done locally and that XML pages without XSLT, or browsers with native XSLT support, are not affected.