Something is wrong with that link that states Your browser is not supported, since even with Safari on a 2022 Mac Studio i get the Your browser is not supported message.
If you want a more modern internet browser, check out Firfox Dynasty, which gives you the most up to date Firefox for older Mac operating systems like Mac OS X 10.11.6 El Capitan.
https://forums.macrumors.com/threads/firefox-dynasty-firefox-for-os-x-10-8-also-web-app-templates.2446475/
You can download the latest Adobe Creative Desktop Application for El Capitan from here:
https://helpx.adobe.com/download-install/apps/download-install-apps/creative-cloud-apps/download-creative-cloud-desktop-app-using-direct-links.html
2008 Mac Pro running Mac OS X El Capitan 10.11.6 with Firefox Dynasty
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