I started playing around with this very recently so I'm super happy to see that you are still updating it. This is an amazing project that got me into the Atari 2600.
A small bug I noticed while using it (browser version) is that the something the changes made in the Player 0 tab don't get saved when I move back to the Actions tab (images I have imported into frames, and the Duration I've set for said frames) In order for those changes to be saved I need to do something else like creating or deleting a new frame.
And a couple of suggestions: Would it be possible to add a block that allows you to mirror player sprites?
And would it be possible to add some sort of blocks, folders or tabs that allow you to group different sections of the code? I'm not very familiar with Blockly but the project I'm currently working on has turned quite big and it's starting to be difficult to keep track of everything and have everything organized.
Thanks in advance, and again, amazing work on this!