Received offer I want to accept, immediately quit recruiting process with other firms?

Hi guys,

Context:
I've been recently made an intership offer at great firm with team I really liked. (Firm A / IB)
It is quite clear to me that I will/want to accept the offer at Firm A.

Around a week ago I had my first interview at a different firm (went good) and got invited to the second round interview, which is in a couple of days. (Firm B / PE)

My question:
Assuming I accept at Firm A today, should I contact Firm B prior to my second interview in order to save both parties valuable time or just finish Firm B's recruiting process and letting them know at the end?

Keep in mind that both firms are in different industries (IB/PE) and I'd be really interested in an internship at Firm B (PE) later on.

Thanks for your advice!