It would indeed be spherical… although zero-g fire has some other odd properties too.
Fighting fire in orbit ain’t something new though: on February 23, 1997 there was a fire in Mir’s emergency oxygen generator (the main system having gone off-line a few months previously).
That one was issuing from the casing of a lithium-perchloride oxygen canister. Accounts appear to differ, with the early reports saying it was a 90 second cigarette lighter deal, with an, ahem, “amendment” to a 14 minute blow-torch emergency after the American crew member returned.
(I’m a fan of the Russian space program, but I think I know who’s telling the tall ones here)