A quick clarification - the output of Webflow actually works across all modern browsers, but the design tool itself has more limited browser support.

One of the biggest challenges with Firefox has been the inability to style native scrollbars to become dark with CSS – theres a decade+ long issue/conversation around making that happen: https://bugzilla.mozilla.org/show_bug.cgi?id=77790. Eventually, we gave up waiting on native support, and now working towards converting scrollbars to be JavaScript-driven to support Firefox (otherwise the white scrollbars stick out like a sore thumb in a dark UI).