Thank you for your review.
Anyway, I will find that bug.

I also think that it takes time to change scrolling speed.
I will plan the way to quick changing.

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Hi renko2. I found why this add-on does not work, but the cause is not the bug of this add-on. "Content Security Policy" decides the source in where scripts are loaded. http://addons.mozilla.org does not permitted the add-on exclude legacy add-ons. Maybe there are some loophole, but I do not seek the way. Sorry.