Permission Denied Error on Firefox mv2

I am running a content script which has an async function that makes an api call to fetch some data like so:
const data = await fethData()
const data = await fethData()
On chrome mv3 this works fine, but on firefox, I keep getting the error
Error: Permission denied to access property "then"
Error: Permission denied to access property "then"
Wondering if anyone has run into this.