Mark css.selectors.selector_list Firefox-supported (#7425)
Mark css.selectors.selector_list Firefox-supported (#7425)

This change marks the `css.selectors.selector_list` feature as supported
in Firefox 84.

implementation_url: https://hg.mozilla.org/mozilla-central/rev/fd29ba131d13

Fixes https://github.com/mdn/browser-compat-data/issues/7408
chrisdavidmills/browser-compat-data,mdn/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data