Install and use a custom Chrome extension in a Browserbase session

Documented steps

1. Package the extension as a .zip with manifest.json at the root of the archive - not nested inside a subfolder. Reference: https://docs.browserbase.com/platform/browser/core-features/browser-extensions
2. Upload it via the SDK: const extension = await bb.extensions.create({ file: fs.createReadStream('extension.zip') }); const extensionId = extension.id. Python: extension = bb.extensions.create(file=f).
3. Direct API equivalent: POST https://api.browserbase.com/v1/extensions with headers X-BB-API-Key and Content-Type: multipart/form-data, binary in the form field file. Reference: https://docs.browserbase.com/reference/api/upload-an-extension
4. Read the HTTP 200 response fields: id, createdAt, updatedAt, fileName, projectId. Persist the id.
5. Create a session referencing it: POST https://api.browserbase.com/v1/sessions with extensionId: "<extension-id>" in the JSON body.
6. Connect with Playwright or Selenium and navigate to a target page to confirm the extension's content script runs (the documented sample modifies page titles).
7. Reuse the same extensionId across future sessions rather than re-uploading the zip each run.
8. Budget extra time in your session-startup timeout, since loading an extension requires a browser restart.