The URL should have the trailing slash. Given the above I would say that
both browsers are broken. The algorithim is supposed to be "deleted back
to the last slash then add the partial URL".
So "http://www.ucr.ac.cr/~mmagallo" + "HTML/html_primer.html" should become
"http://www.ucr.ac.cr/HTML/html_primer.html" (note that ~mmagallo gets
dropped). At least that is my understanding.
Think about it like this, "http://www.ucr.ac.cr/~mmagallo/" is *really*
supposed to be like "http://www.ucr.ac.cr/~mmagallo/index.html" (maybe
yours isn't called index.html or maybe it's generated on the fly, doesn't
matter--this is just an explination of how and why).
Some servers will reject access to a directory without a trailing
slash (they issue a redirect the client to correct it). But, in
general, a directory access should have a trailing slash.
--sanders