List extensions that are opened with a specific application
If you want all files with a certain extension (not the 1 specific file) to be opened by a certain app, do the following:


Right click the file and click Get Info (or highlight file and hit cmd ⌘ + i )
Change Open with: to preferred app
Click Change All...
Click Continue in the confirmation box


Is this what you meant to do? This is different from right clicking a file and choosing the 'Always open with' option. That seems to only apply to the specific file, not all files globally.

You will have to repeat this for each extension.