There are a wide variety of login plugins on the plugins page
Additionally, you can bookmark the login script and add a loginname parameter that will automatically fill in the username on the form, like this:
You can use the above format with WindowsMailto to make Windows load up SquirrelMail when you click on a mailto: link.
You can do an ever "quicker" login by using the following:
1. You are including your password on this line, and it is therefore a security risk. Anyone using your computer can now access your mailbox, and know your password.
2. This is all one line of text - but it is so long your display is probably displaying it as multiple lines.