It works well once you get it working. I had a bit of trouble getting it to see my Mastodon session. Here's a tip: Remove the slash at the end of the URL. It won't work if that slash is there.

Another issue is that it only works on webpages and not images. Meaning that it would post a link to the image and not the image itself. If it would actually post an image that would be great.

This extension does not use the Mastodon API, instead it opens a new tab to share something, and it fills the text input in your web interface of your Mastodon instance.
I would prefer a popup with just a pre-filled form with the URL of my resource and the title, or the text I selected.
But it works and does the job ;)