When you search using Firefox’s Search form, it’ll automatically open the queries in the same tab that was open. This behavior can be annoying, but luckily there’s an about:config setting to tell Firefox to open searches in a new tab.
Head over to about:config in the location bar, then type the following in Filter:
browser.search.openintab
Double click it so that the value becomes true, then restart Firefox.
ALT+ENTER opens in a new tab as well.
Alan: Ah, thanks, I was unaware of that. I used to just open new tabs or middle click the search button.