To address the concern around the newly requested permission for Website Content (which also freaked me out), the code is posted on GitHub. I checked the changes, the change was made by the same guy who has been developing this since early 2023. Nothing malicious was added to the code and the data type is not what we all think it is. Here is the definition Firefox provide for the Website Content permission:
"Covers anything visible on a website – such as text, images, videos and links – as well as anything embedded like cookies, audio, page headers, request and response information."
I'd emphasize that this is separate from the Browsing Activity category, which this plugin does not ask for. The very next change committed was a check whether the game is in your library, so it is possible the permissions were for this:

"in_library": {
"message": "In Library",
"description": "Indicates that the user owns this product"
},

That being said, it would have been good if the dev explicitly clarified why the permission request is there, either on the extension install page or within GitHub to put everyone's mind at ease.