$ ./Meta/ladybird.sh run WebDriver
...
Listening on 0.0.0.0:8000

First request works fine, opens the window and receives a session ID of 0:

$ curl -d '{"capabilities":{}}' http://127.0.0.1:8000/session
{"value":{"sessionId":"0","capabilities":{"browserName":"ladybird","browserVersion":"1.0","platformName":"linux","acceptInsecureCerts":false,"strictFileInteractability":false,"setWindowRect":true,"serenity:ladybird":{"headless":false},"pageLoadStrategy":"normal","timeouts":{"script":30000,"pageLoad":300000,"implicit":0},"unhandledPromptBehavior":"dismiss and notify"}}}

Second request opens a new tab but never gets a response:

$ curl -d '{"capabilities":{}}' http://127.0.0.1:8000/session
...hangs...

Deleting the existing session either before or after the second POST works in that it gets a response but doesn't prevent future hangs:

$ curl -XDELETE http://127.0.0.1:8000/session/0
{"value":null}