19 October 2021
Most modern websites are no longer accessible to early Mac OS internet browsers. This is a result of the rapid advancement of web/web development standards, many of which which were not present in browsers during their time of release. Modern websites are usually served through the HTTPS protocol, which is incompatible with many older browsers that only support the insecure HTTP protocol. For more information on this issue, you can read about HTTPS and why it's a problem for early Mac OS.
Websites that have been designed with older browsers in mind, or ones that have remained online since the early 2000s can still be accessed on most browsers.
There has been an effort to compile a directory of modern and existing websites that are accessible to older web browsers. See the Sloop Website Directory.
Classilla was the last web browser that received recent updates and was maintained regularly until 2021 by Cameron Kaiser. The only downside to using Classilla is that it is resource hungry and requires later Mac OS versions. Classilla requires a G3 Processor, 64MB ram (minimum) and Mac OS 8.6.
Internet Explorer 5 is the next best browser for older Macintosh systems. During it's time IE5 for Mac was one of the best web browsers available, and was still relatively usable throughout the 2000's. IE5 uses minimal system resources and runs on Systems 7 - 9.2.2.