Single Window mode
Do you hate it when links on Web pages open new windows (because they set a target attribute on the link)? You can force Firefox to open those links in a new tab instead of a new window. This is called Single Window mode. It doesn't prevent all new windows, but it catches most of them. The radio buttons for setting this preference are in the Preferences window, but only if Firefox knows you want to see them. Go to About:config and set browser.tabs.showSingleWindowModePrefs to true.
Once that is done...
- Go Tools - Options - Tabs
- Select Checkbox beside "Force links that open new windows to open in:"
- Choose "a new tab" radio button.
- Hit 'Ok' and your done!