As of Firefox 7, Mozilla has disabled the http:// prefix from displaying by default. I personally found this to be annoying so I decided to change the setting back.
If you’re trying to change this setting, you’ve probably already noticed that it isn’t in the in the normal Firefox options menu. For this setting, you’ll have to navigate to about:config by typing that in your Firefox address bar just like you would do with a normal address.
You’ll be prompted to accept a warning and will then be taken to a list of hundreds of preferences.
The setting that you need to toggle is called browser.urlbar.trimURLs. You can either scroll down to find that option, or paste the name into the filter box above the list of options.
Once you’ve found the browser.urlbar.trimURLs preference, you need to change it to false. You can do this by right-clicking and selecting “Toggle”, or by simply double-clicking.
That’s it! There’s no need to restart Firefox, you should now see the http:// prefix in all open tabs.