Question: How does simplify.jobs form filling feature work behind the scenes?

Hi, I'm wondering what libraries or frameworks they use to make it happen. I've been trying to make a similar form automation Chrome extension using Selenium, but it hasn't been working exactly the same.

According to a reddit reponse I found: "We use Next.js for our frontend, FastAPI on our backend, and our extension is in Typescript. All backend services are deployed on GCP."