One thing I’ve noticed is that some tools are incompatible with an XHTML5 MIME type. Site auditors like Lighthouse are only provisionally compatible, and some browser extensions are rather buggy. You can compare them yourself on seirdy.one: switch the MIME type by appending /index.xhtml to a URL. You may have to disable the CSP sandbox by appending ?sandbox=off to the URL to get Lighthouse to work. I keep my site polygot and serve with the text/html MIME type by default for maximum compatib...
