I am not sure if 'unmasking' is possible, I believe some browsers don't allow changing of password fields to regular text fields for security concerns. Honestly I don't think it is a big problem that you can't see the characters you type - basically every other website in the world does the same and it works fine for them.
As for those websites, the software we use (Question2Answer) is loosely based on their system. Stack Overflow etc use their own original system, not Q2A. They kind of revolutionised the Q&A format and were the inspiration for me starting this site.