Set Default File Viewer

Once Cosmil is your default file viewer, other apps open Cosmil instead of Finder when you choose Show/Open/Reveal in Finder. Folders you open from other apps or from Terminal also open in Cosmil. The Desktop is the one exception, because Finder always runs it.

Note

Unfortunately, Finder's Open/Save file dialogs are hardcoded to use Finder by macOS — because of this they cannot be replaced by Cosmil or any 3rd party app.

Open Terminal

Paste the following commands and press Return:

defaults write -g NSFileViewer -string app.cosmil.explorer;
defaults write com.apple.LaunchServices/com.apple.launchservices.secure LSHandlers -array-add '{LSHandlerContentType="public.folder";LSHandlerRoleAll="app.cosmil.explorer";}'

Restart Your Mac

Check that it worked#

In the Terminal, run open ~/Documents. Your Documents folder should open in Cosmil.
In Safari, open your downloads list and click the magnifying glass next to a download. Cosmil should open with that file selected.

Switch back to Finder#

Paste these commands into Terminal, press Return, then restart your Mac:

defaults delete -g NSFileViewer
defaults write com.apple.LaunchServices/com.apple.launchservices.secure LSHandlers -array-add '{LSHandlerContentType="public.folder";LSHandlerRoleAll="com.apple.finder";}'