>>972
わざわざ、アドオン入れていただいて有難うございます。
確かにタブエディタだと上手くいきますね。
ただ、起動するアプリは、画像ソフトから、この5chブラウザまで色々あるので、
何とかアドオンかUWSC側で出来ないかと探していたら公式のFAQにこんなのが書いてありました。

[Firefox Only] When I close my Firefox browser, all the applications that have been executed from this extension also get closed.
Why is this happening? Can I somehow keep them even after Firefox is closed?

This is due to how Firefox handles native applications.
Since all native process that gets started by Firefox is considered to be a child process of Firefox,
your operating system (Windows only) closes all these child processes once the parent process is killed or closed.
There is no simple way to bypass this restriction, however, there is a native program that can be called to change the parent process of a child process.
It is called RunFromProcess by nirsoft. You can call this application instead of your native one and ask the RunFromProcess to assign another process for the application to be opened.
This way when Firefox is closed, the child process is not being killed since its parent is still alive.
Make sure to set a parent that is a persistent process like "explorer.exe" for instance.

要は、RunFromProcessを使えば出来るけど、そう簡単ではないぞと。

確かに、簡単ではない、、　orz