Ask HN: How do you develop sites targeting IE in 2019?

For various reasons, I have to support IE (11) in my work on a large React/Redux/Bootstrap app, using fairly standard Babel transpiration and polyfills.

I’m interested to hear how others in similar situations manage this problem - questions like:

Do you develop IE-first or have it as part of a testing checklist?

What have you learned about performance optimization for the IE VM?

Are there alternatives to the very slow F12 devtools?

And any other tips you’ve collected while supporting the browser.