Persist Extensions on launch

```jsonc
{
// Use IntelliSense to learn about possible attributes.
// Hover to view descriptions of existing attributes.
// For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
"version": "0.2.0",
"configurations": [
{
"name": "Hello",
"type": "firefox",
"request": "launch",
"reAttach": true,
"url": "http://localhost:4000/",
}
]
}

```

Under launch mode, a fresh Firefox instance is opened, one with no account synced and no extensions.
Is there an override or anything of some sort that lets "launch" launch a browser instance that's just like a regular launch with remote debugging enabled?

No source file or test is named. Start by tracing how launch configurations create a fresh Firefox instance and handle the reAttach option; done means launch can use a regular Firefox profile with synced account state and extensions while retaining remote debugging, with the behavior covered by an appropriate test.

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