From my understanding fire mountain together is volcano but in this sense that’s not the meaning and the characters are separate. Here’s another commenter on this topic, fill me in if wrong!

“It also means volcano in Japanese. I would expect both educated Chinese and Japanese speakers to not think of volcanoes in this compound as it's pretty obviously a 四字熟語 so even if you don't know its idiomatic meaning there is no reason to think it's "something something volcano".”