Thanks for using my extension! I appreciate and have considered your suggestion, but I won't add it.

This feature would essentially only remove the step of opening a new tab of the selected page. Since this only takes two mouse clicks (click URL bar to select it, drag selection to tab area) I don't think it adds much value on its own.
I considered the possibility to clone a tab including its state, meaning for example keeping text input in fields, but I've looked into it and it isn't possible.

There is a setting in the Workarounds section to add/subtract pixels when calculating how to place and size popups.
For example: if you have a rule that sets x=0 and width=100, and use this setting to add 10 to X and subtract 20 from the width, the result simulates a 10 pixel gap on the left and right sides.

Note that this only applies when the popup is opened and placed by the extension, **it's not possible to add a real invisible border** to a window from an extension. If you use for example Windows Snap afterwards then the popup will not have a gap between itself and the other window.

Edit: Sorry, I still don't understand what you are asking for, can you clarify? This is what I refer to as "invisible border": https://i.imgur.com/3fEz63K.png (It's only a problem in Windows 10 as far as I know)
(Edit 2): Maybe I understand... Do you mean the title bar that's supposed to be to the left of the minimize/maximize/close buttons but is gone in your image? That's not something I am explicitly able to hide, and I don't want to add features that relies on bugs in order to work.

谢谢。我不懂中文。 英语好吗？

I want to keep the add-on simple, gestures is a separate and hard problem. I suggest that you contact the developer of a mouse gesture add-on and ask them to add a popup function.

Otherwise I can add an API that another add-on can use, please ask the add-on developer to contact me in that case.