I was getting irritated while I was unable to click on the URLs found on many of the applications on my Ubuntu desktop. I remember opening such URLs on my default browser Firefox. No idea when the settings were modified.It might sound so silly issue to be documented but, I was in bad state when my hands were full with work and URLs needed me to copy the source and put them on address bar each time. At last I found a quickie. Never thought I won’t recall this menu when needed.
Ubuntu has got a simply way of setting default applications for Multimedia, Internet, System, Accessibility etc. Just follow the menus System -> Preferences -> Preferred Applications.
Too simple isn’t it? Thats why they call Ubuntu as – Linux for human beings 
If you use Firefox as default browser, you can instruct your system to open the new URL in a new tab.window too.