I strongly resist the term "normal". Because it means such different things to different people. And do you have a problem? No. You don't have a problem!
As with any fetish or paraphilia. I think it's sensible to be cautious who you talk to about it. Not everyone needs to know every detail of someone's sex life. [In fact, that's probably a paraphilia in itself.] Some people might not be cool about it. But that's all the worry I'd have. Plus be honest too. Don't steal sneakers to masturbate with! Use Ebay or charity shops if you find that you have urges for strangers' shoes.
But there's nothing wrong with it or with you. That's part of what you get off on, that's fine.

We all like different things. And as long as no-one is being [unwillingly] harmed. It's all good.