Add export FZF_BASE=~/.oh-my-zsh/plugins before plugins line in .zshrc
Also for Ubuntu you can install .deb package by Launchpad link: http://launchpadlibrarian.net/456699009/fzf_0.20.0-1_amd64.deb
Also for Ubuntu you can install .deb package by Launchpad link: http://launchpadlibrarian.net/456699009/fzf_0.20.0-1_amd64.deb