Open Typed URLs in New Tabs

Everyone is probably aware of how to open links in new tabs in your favorite browser--just Command-click the link, and it will open in a new tab, instead of replacing your current window's contents. (This is a great way, for example, to browse the Macworld news page and open all the stories you'd like to read without losing the news page.)
But what if you're typing a URL, and you'd like it to open in a new tab? If you're using Safari, Camino, or OmniWeb, all you need to do is hold down the Command key prior to pressing Return after typing the URL. All three browsers will open the typed URL in a new tab, and will respect your preferences settings relative to new tab behavior--if you've got the preferences set to open new tabs in the background, then that's what will happen, and vice versa. (You can use this same trick in the Google search box, too.)
Firefox, however, is different. Instead of using Command-Return, you'll need to hold down Option and then press Return. This will force the URL to open in a new tab. Unfortunately, that new tab will open in the foreground, regardless of your preference settings. As I much prefer new tabs to open in the background (so I can continue reading the foreground tab), I went looking for a solution. I found that solution in a Firefox add-on called Tab Mix Plus. Unfortunately, that linked version won't work in Firefox 3, so I had to do further digging. Over in the Tab Mix Plus forums, this thread contains links to developer builds that work with Firefox 3.
As of today, the top post in that forum links to Tab Mix Plus Dev Build 0.3.7pre.080721, which works fine on my Firefox 3.0.1 installation. To install it, just click the Dev-Build link in that first forum post. Firefox will display a message stating that installation has been blocked. Click Allow to go ahead and install the extension, then restart Firefox.
Once Firefox restarts, open its preferences and select the Tabs tab. Click the Tab Mix Plus Options button, then click on the Tab Focus tab in the new window that opens. In the section labeled 'Focus/Select tabs that open from,' remove the checkmark next to Address Bar. If you'd like to use this same trick in the Google search box, also remove the checkmark next to Search Bar. When done, click OK and close Firefox's preferences panel.
From now on, when you press Option-Return after typing in the URL bar (or search box), Firefox will open the resulting web page (or search results) in a new background tab।
Reference : http://www.pcworld.com/article/148870/2008/07/.html?tk=rss_news