When I dismiss alerts after logging in, they show up again the next time I log in.

The normal behavior after clicking “Don’t show this again” on an alert is the alert stays gone the next time you log in. Cookies are used to accomplish this. If the alerts keep returning, it could be your browser is set to clear your cache/cookies/temp files every time you close it, or set to not accept cookies. Please check your browser settings to see if something like this is going on.

See Also
How do I get rid of the Service Hours Setup Alert?