Could you please check if the button appears on any of these:
https://upload.wikimedia.org/wikipedia/commons/8/87/Schlossbergbahn.webm
https://upload.wikimedia.org/wikipedia/commons/3/39/Lichtenstein_img_processing_test.png

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I know I'm telling this every time, but try deleting and installing this extension again.
I'm gonna make proper settings reset/import/export functions in next update, so it probably would be much easier to debug problems like this one. But for now reinstalling would be the fastest solution.

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Never thought someone uses this mode, as it said, it's experimental. Thanks for letting me know, will try to fix this option soon.