Generally, when an adjective is derived from a proper noun, the adjective also has a capital initial, hence Googleable, Mancunian, British, and Shavian. (In contrast, verbs are not given capitals, hence to google and to hoover.) For some reason, though, biblical is an exception. The word Bible itself can be used as a normal noun (the fisherman’s bible, or a bible for cooks), but biblical clearly refers to the proper-noun usage of Bible, and yet it is not given a capital initial. Why is this?
(Actually, a minority of dictionaries do give a capital initial, but that usage is rare in my experience.)