See "Submit automatically after filling a Login (Autosubmit)", "Fill Login keyboard shortcut", and "Go & Fill keyboard shortcut" under Login Options in the Logins tab of Preferences. Also check the documentation; Help > 1Password Help opens it in a browser.
1P's lack of support for "Safari-style" autofill (which I happen to like) is intentional. I think it's for security-related reasons though I don't recall specific details, only that the topic has been previously discussed (edit: e.g., in: Why can't 1Password automatically fill in fields?).
We actually have a great feature in 1Password which might help you here. If you open up 1Password and locate a login you want to have a bookmark for you can then drag this item to the Firefox bookmark bar and then click this to have the same behaviour as you would see using the 'Go & Fill' option. We call this a '1 Click Bookmark' and you can read more about this in our user guide here:http://help.agile.ws/1Password3/oneclick_bookmarks.html
Hope that helps,