By design? Or running code in the browser is inefficient? (not your fault, that's the way it is) Keepass (Desktop app) for example doesn't take ages to open.
Yes: By design. This helps make brute forcing the password harder by forcing each attempt to take a while. The crypto implementation in the browser itself is pretty fast.
You can easily make it faster or instantaneous by lowering the number of PBKDF2 rounds in the html-vault script. The default of 20 million seems a bit excessive based on the feedback so far.
