Thank you for this report. I believe Firefox does have *some* limit on the size of an image it will draw on or extract from an HTML canvas (which is how the conversion is done). Still, 8190 seems too short, since my test image is 720x22000 and that one works fine when I open it stand-alone in a tab.

When you are saving the image in its original page, I wonder whether a style rule can affect the height? Maybe you can send me an example URL of where the problem occurs, either in a new issue at https://github.com/jscher2000/Save-webP-as-extension/issues/ or by email at jscher2000@outlook.com.