First, we should comment that this is a strange thing to want to do. WebMask is principally designed to remove banner adverts - graphics which Lynx users are fortunate enough not to see anyway.
However, WebMask can block HTML files as well, so Lynx users may have a use for it. For those who want to try, here are the instructions:
Find the lynx.cfg file - this is usually in your Lynx directory on Win32 machines.
Edit lynx.cfg, and search for http_proxy. If you haven't set a proxy before, then this line will be commented out with a #.
If the line wasn't commented out, then you need to write down the host and the port that it is currently set to use. The host is the name of the computer between the // and the last :, the port is the number after the last :, or 8080 if none is specified. Later you will use these to tell WebMask about this existing proxy.
Change the http_proxy line to read:
Setting up your browser to use WebMask