- Open a new tab with Ctrl-T
- Click into the URL address bar
- Paste the URI and press Enter
Firefox has this possibility, but you can't enable it from the normal preference dialog.
Instead you have to alter the configuration parameters directly.
- Navigate to about:config
- Put middlemouse.contentLoadURL in the filter bar
- Press the right mouse button over the option and select toggle, so it's value is true.
- select and copy this text: www.ubuntu.com
- press the middle mouse button in the window where you're reading this post
- A new browser tab should appear with the Ubuntu site.