(/.*)? is for the version number, just like pascal explained.
I did consider using full version patten, but not sure if the version pattern won't change in the future.

As for the optional trailing slash, (with an end of string anchor?)
I suppose any paths prefixed with firefox/firstrun (or tour, whatsnew) might be in-product pages,
and those paths are better left in mozilla.org.
Since mozilla.com.tw no longer maintain up-to-date in-product pages.