I come across this annoyance every time I upgrade from Firefox 1.5 to 2.0, but keep forgetting about it.
In FF 2.0, there is no option to force every new link, which would open a new window, to open in a tab. I would think that the option under Preferences >> Tabs for New pages should be opened in: a) a new window or b) a new tab would do this, but it doesn’t. Oh well.
Today, I had to upgrade someone else’s Firefox and this issue came up again. Doing a quick Google search gave me the answer.
Go to about:config. Look at the image below and set the preferences to the following values:
Its that simple.