Generally, software support for Lion is becoming scarce and an alternative solution will soon be necessary. However, there are a few years before that will happen. The main concern is when websites no longer support these older browsers.
Though there are 'security risks' with using Lion to browse the net, I haven't had any problems. Opera is built on Chrome's Chromium webkit engine so Opera support was also cut around the same time as Chrome. The default Safari browser hasn't been updated since 2014.
Chrome supported Lion until April of 2016 while Firefox supported it until August 2016. As of this writing, no major browsers support Lion.
