Go at http://ftp.gnu.org/gnu/gnuzilla/ and download the latest package.
Extract it at your desired location.
There, you may be able to launch the browser by just double clicking the icecat executable, or try first, by opening a terminal in that location:
chmod +x icecat
To create a desktop file like for a normally installed browser:
Using gedit text editor:
sudo gedit /usr/share/applications/icecat.desktop
Then paste this, changing accordingly the lines that start with Exex= and Icon= :
[Desktop Entry]
Name=Icecat Web Browser
Keywords=Internet;WWW;Browser;Web;Explorer
Exec=path/to/your/location/icecat %u
Terminal=false
X-MultipleArgs=false
Type=Application
Icon=path/to/some/icecat.png
Categories=GNOME;GTK;Network;WebBrowser;
MimeType=text/html;text/xml;application/xhtml+xml;application/xml;application/rss+xml;application/rdf+xml;image/gif;image/jpeg;image/png;x-scheme-handler/http;x-scheme-handler/https;x-scheme-handler/ftp;x-scheme-handler/chrome;video/webm;application/x-xpinstall;
StartupNotify=true
Actions=NewWindow;NewPrivateWindow;
Save, close, and you should see it in Dash or other launchers, or add it to a panel etc.
Depending on your desktop environment and/or launcher: in order to properly see the icon in the launcher, icecat.png file might be needed in a proper location.
Let's say we have a 128x128 file called icecat.png (that we can get from somewhere like here).
Go to the location ~/.local/share/icons/hicolor/128x128/apps/icecat.png ( or create it first), and then again sudo gedit /usr/share/applications/icecat.desktop, change the necessary line to Icon=icecat.