l-switch

l-switch is the Firefox client for pm-switch: a developer tool for running local front-end code against real production or staging APIs.

Modern browsers enforce CHIPS (Cookies Having Independent Partitioned State). After CHIPS, whether a cookie is sent depends not only on Domain and SameSite, but also on the cookie’s partition (the top-level site context). A simple in-browser redirect from localhost to an online host is often not enough—partitioned cookies may not ride along automatically.

l-switch handles that for you: when a proxy rule matches, it reads partitioned cookies for the target site and injects them (and related headers such as CSRF tokens) into the proxied request, so your local app can still call authenticated online backends.

Key features

• CHIPS / partitioned cookie support — Uses cookies API with partition awareness and injects the right cookies on redirected traffic (see getPartitionCookie in the extension).
• URL proxy rules — src → tgt matching (string or regex).
• Header helpers — Referer, Origin, optional headersToAdd / headersToDel, and cors host lists for cross-origin scripts after redirect.
• JSON configuration — Edit rules in the popup; toggle the toolbar switch to enable or disable.

Who it is for

Front-end and full-stack developers who:

• Develop on localhost (or another local origin) but need live backend responses
• Rely on partitioned (CHIPS) cookies for login/session on the target domain
• Want the xswitch / pm-switch workflow without manually copying cookies

1. Open the popup and edit JSON (proxy, optional cors).
2. Turn the extension on.
3. Reload your app; use credentials: "include" on fetches when cookies are required.

{
  "proxy": [
    {
      "src": "http://127.0.0.1:7001/(.*)\.json",
      "tgt": "<a href="https://prod.outgoing.prod.webservices.mozgcp.net/v1/b6a74d1010abdeb5d19016e88f4b5316c2d5222ff5561ef932d18ac93a03bb12/https%3A//example.com/%241.json" rel="nofollow">https://example.com/$1.json</a>",
      "headersToAdd": [
        {
          "headerName": "X-Xsrf-Token",
          "fromCookieName": "XSRF-TOKEN"
        }
      ]
    }
  ],
  "cors": ["<a href="https://prod.outgoing.prod.webservices.mozgcp.net/v1/2141eac2eacda036b00afc30fd0a7e6f24e9bddf402cf4393fe5144f468147e8/http%3A//example.com" rel="nofollow">example.com</a>"]
}