I'm sorry to say that installing version 6.1 of MIRC didn't solve the default browser problem for me. I'm sad.
I use Crazy Browser
and even after the recent install of 6.1 I still have IE opening when I click on a link in a channel.
If I click on a .HTML or .HTM file on my desktop Crazy Browser opens as it should. Also if I click on a link in an e-mail or an instant messanger window Crazy Browser opens.
Only MIRC seems to have this problem. I've tested this on two computers, both Win2k, both had the previous version of mirc on them and had mirc 6.1 installed into the same directory keeping the settings. Both have Crazy Browser installed as their default broswer, but both get IE when a link is clicked in MIRC.