sudo mv ~/Downloads/Zotero_linux-i686/ /opt


zotero.desktop
#!/usr/bin/env xdg-open
[Desktop Entry]
Type=Application
Name=Zotero
GenericName=Bibliography Manager
Icon=/opt/Zotero_linux-x86_64/chrome/icons/default/default48.png
Exec= /opt/Zotero_linux-x86_64/zotero %f
Categories=Office
Terminal=false

sudo mv zotero.desktop /usr/share/applications


To uninstall: sudo rm -r /opt/Zotero_linux-x86_64 and sudo rm /usr/share/applications/zotero.desktop. User files are in ~/.zotero.