How do I stop mouse movement from affecting "isMouseButtonDown"?

Here's a video to give some context to the issue.

I'm trying to make a first person shooter as part of a class I'm taking. And the actual "firing" part is fine; however, whenever I move my mouse, the firing animation (and actual firing) is interrupted. Which is... kind of important.

Here is some of my code:

You have to disable 'Unadjusted movement' in 'Request pointer lock'. This is only necessary if you need the raw mouse movement data.