This problem most likely has to do with storing Cookies on your computer. If you disable cookies, you'll have to enter your username and password every time you open your browser.
The easiest way to solve this problem:
- Go to Open menu (top right corner)
- Choose Options > Privacy & Security
- Look for the option Cookies and Site data.
- Make sure you 'Accept cookies and site data from websites (recommended).'
- Keep until 'They expire'
- And finally 'Accept third-party and site data. Alway.'