The chance of your ballot being burned by an arsonist are near zero. if you want to vote, and a drop box is near you, then that's totally fine.
If you are worried about it counting go to the MyVote Oregon page and set it up to track your ballot. https://sos.oregon.gov/voting/Pages/myvote.aspx?lang=en
All of this talk of how it's "unsafe", we need more cops, blah blah blah will just scare people away.
You are almost certainly just fine, and if you are concerned, then you can just track it. No need to worry or panic about anything.