[SOLVED] I can't run Element web in mozilla-firefox-115.13.0esr-x86_64-1_slack15.0

I don't know if it's due to my settings or what, but browsing https://app.element.io/ I now get this message:

Quote:

Unsupported browser Your browser can't run Element Element uses many advanced browser features, some of which are not available or experimental in your current browser. Please install Chrome, Firefox, or Safari for the best experience.

This is in Slint64-15.0, based on Slackware64-15.0. Does Element web work for someone else using the same Firefox version in Slackware 15.0?