Opera has a "Next Page" feature that is usually able to do exactly what you ask on most sites/forums. Also, it's smart about it - if you're on a page that it's

Opera has a "Next Page" feature that is usually able to do exactly what you ask on most sites/forums. Also, it's smart about it - if you're on a page that it's remembered a username/password for, if you go Next Page (either the mouse gesture or left/right mouse rocker gesture), it'll log you in automatically.