In the Mac port there's a menu to enable the experimental features listed in: https://github.com/WebKit/WebKit/blob/main/Source/WebCore/features.json This allows people to play with the features easily on a regular build. It'd be nice to add support to enable these features in GTK and WPE ports too. One idea could be to add a page like about:config in Firefox or chrome://flags/ in Chromium that would provide a way to enable/disable such flags for minibrowser/cog/epiphany in the same way.