Sorry, WebExtentionsApi can not undo close tab on Firefox for Android.
(Because, the "sessions" api is not supported.)
Thank you for your review.

You can pageUp and pageDown with custom-gesture.

Try these code.
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/** @name pageUp */
window.scrollByPages(-1, { behavior: 'smooth' });
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/** @name pageDown */
window.scrollByPages(1, { behavior: 'smooth' });
------------------------------

Thanks.

Sorry, I couldn't find the way to go fullscreen.

Video files (e.g. "*.webm") will cancel fullscreen, if execute this code with Custom-gesture.
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/** @name Cancel fullscreen */
document.mozFullScreenElement && document.mozCancelFullScreen();
---------------------------------------------------------------------------

Thanks.

ok, I add it at version 1.5
thx.