Uninstalling other fzf plugins

fzf.fish is incompatible with other fzf plugins for fish.

fzf's out of the box fish extension

You probably installed it when you ran its installer. Uninstall by running the uninstaller. It may already exist on your system. For homebrew specifically,

cd (brew --prefix)
/opt/fzf/uninstall

If you can't find the uninstaller on your system, you should be able to download it and execute it locally.

jethrokuan/fzf

Uninstall with fisher remove jethokuan/fzf if you installed using fisher.