Sorry, that has two probrems.
･Webextensions doesn't work special tab. so, you must open "about:tabs" manually for select other tab. (and, you can close special tab in "about:tabs" manually.)
･Webextensions API sometimes returns "about:blank" instead of actual URL.
thx.

p.s.
I planning wrap "browser.tabs.query({});" by "SimpleGesture.getTabs();"