As mentioned elsewhere on the forum, I used the command lineto force window-opening links into tabs. Since then, however, I've been annoyed by popup ads (which are supposed to be blocked anyway) which are written to open a fixed-size, toolbar-less, scrollbar-less window. http://www.boston.com has one, and http://espn.go.com sometimes does as well. It forces my main browser window to a new size, and takes away the toolbars and scrollbars. Amazingly annoying, as you can imagine.
defaults write com.omnigroup.OmniWeb5 OWOpenNewFramesInTabs -bool true