your wrangler.toml should be like:

name = "browser-worker"
main = "src/index.ts"
compatibility_date = "2023-03-14"
node_compat = true
workers_dev = true

browser = { binding = "MYBROWSER", type = "browser" }

Make sure you're not trying to test locally as well. If you're on the latest wrangler/wrangler@3, use

npx wrangler dev --remote