Britain is the land mass that includes England, Wales, and Scotland.
William the Conquerer was the first Norman king of England and never had power over Wales and he was mostly successful in gaining homage from King Malcolm III, but never king over the lands.
Edward I about two hundred years later almost pulls it off, but doesn't quite get a firm grip on Scotland. James I in the early 17th century holds the crown for each of the lands. In 1707 they formalize the relationship with a treaty.
So... No the French did not found Britain.
Can you put the relevant comment link in the OP?