[thro1]

Gecko currently has much deeper integration of the XSLT engine with the browser internals: The XSLT engine operates on the browser DOM implementation. WebKit and Chromium integrate with libxslt in a way that's inherently bad for performance ( https://github.com/whatwg/html/issues/11578#issuecomment-321... )

Just Firefox XSLT is faster, better than Google's (and JS), same, old Firefox extensions were to powerful Google could compete with Firefox.

JS is very needed for ads, tracking and other strings attaching - and XSLT is not for that - but would make JS mostly obsolete in many cases.. (only "cross-browser functionality for XSLT is incomplete with certain features like <xsl:text disable-output-escaping="yes"> having open issues" ).

Google pay Mozilla to criple Firefox. It's money from ads, to not let the web be free.