The command to open (for example) /home/user/html/file.html in konqueror is
Code:
/usr/bin/konqueror --profile webbrowsing file:///home/user/html/file.html
To open it in Firefox (adjust to your path, of course):
Code:
/usr/local/bin/firefox file:///home/user/html/file.html
I don't know if it's necessary to specify the path or not. I haven't used KDE for a while.