Sure it may be easy to have your browser remember your ID and passwords for you. After all, you have so many different combinations that you have to keep up with. But, this is a big security issue if anyone should ever get into your computer. There are tools that technicians use to help recover passwords, but some browsers make it just too easy. There was recently a lot of news coverage on how easy it is with Chrome, but Firefox and the others are all suspect to the same type of exposure.
There are some other options that can help make it easy and secure at the same time. Options like KeePass and LastPass are just a few. I have been reviewing LastPass and will try out KeePass also. Once I finish my reviews, I will post my findings. They both are better options than having your browser store the passwords, or the most dreaded practice of having all your ID and passwords be the same.