Our secure website is based on Drupal, an open source content management system, secured with a "Lets Encrypt SSL" certificate, and hosted by Fluccs
It is probably best viewed with a Firefox browser, as that is what the maintainer uses, but should work on any modern browser. As well as Firefox (on linux) it is regularly checked with Firefox on Andorid, Windows 10 and Windows XP, the current Microsoft browser on Windows 10, and the native browsers on Android. It doesn't do anything particularly bizarre, so it should "behave" on any reasonably recent browser.
There are, however, some problems on older (seriously older) browsers. The layout manager is based on html 5, and not all older browsers handle that correctly, though it is usable (if not as pretty) even on IE8 on XP.
The other problem with older browsers is the certificate. Because it is a hosted site, not a distinct server, the certificate uses "Server Name Indication", which is not supported by some older browsers. Also, some older browsers may not recognise "Lets Encrypt" as a certificate signing authority. Either of these cases may lead to messages like "The security certificate presented by this website was not issued by a trusted certificate authority" and/or "The security certificate presented by this website was issued for a different website's address" (as from IE8 on XP). If you get these messages, it is time to upgrade - it will not only be our site that will give these problems. Firefox ESR is still available for XP, does not have this problem, and is downloadable from Mozilla.