I really enjoy the look of UBUNTU. The only thing that I want to change is the default icon used for .html (.htm) files. I want to use the icon /usr/lib/firefox/browser/icons/mozicon128.png instead. I do not want to change any other visual element. Is there a practical way to accomplish this small change?

edit: @Mitch, I've used assogiate in the past and although I was able to change the icon used for .mht files, I could not get it to change the .htm icon. @Anwar Shah, thanks for the information. I wish that it would work for me. Running 13.10 x86, after I do the copy of the icons, in the folders are a bunch of links to .svg files not actual graphics files. It does not appear that the second copy actually does anything on my system.