Add information of base Firefox version to about page

[Yuki2718]

Currently only the version of Floorp is shown.

Screenshot

If you want to know the Firefox version it is based on, you have to go through about:config or something. Someone even asked the version in Discussion. Brave shows its base Chromium verison like version: 1.63.165 Chromium: 122.0.6261.94 and this is convenient for other developers when they see reports with browser version if there are known issues on certain version of Chromium.

[CutterKnife]

about:preferences で確認できますが、確かに "Floorp について" にあれば便利かもしれませんね。

[regularentropy]

You can check it in about:preferences