Old versions of Internet Explorer that shipped with Windows XP might still work. So might old versions of Firefox which can still be obtained from the Mozilla FTP servers.
Regarding the meaning of "perpetual license", the reasoning is laid out at e.g. https://www.millisecond.com/products/faq.aspx, quoted below for convenience:
A perpetual web license does not expire, so you may continue using it as long as you like. However, at some point in the future we will stop releasing updates for it, which means the underlying technology may eventually become obsolete as newer versions of browsers and operating systems are released. For this reason, we offer steep discounts to perpetual license holders who wish to upgrade to a newer version of Inquisit."