Q4 what's newsletter (#528)

docs/whats-news/2023/2023-q4.mdx

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+---
+id: 2023-Q4
+title: What's New in Nimbus - Q4 2023
+slug: /whats-news/2023-Q4
+sidebar_label: What's Newsletter Q4 2023
+---
+
+## Mobile 
+
+Coming soon...
+
+## Desktop
+
+Coming soon...
+
+## Jetstream & Results Analysis
+
+Coming soon...
+
+## Cirrus
+
+Coming soon...
+
+## Experimenter
+
+🙌 FML error detection - [EXP-3873](https://mozilla-hub.atlassian.net/browse/EXP-3873), [EXP-2365](https://mozilla-hub.atlassian.net/browse/EXP-2365)
+
+   > Error detection using the Feature Manifest Language is now available in Experimenter! For all applications that utilize the FML (non-desktop apps), the "Branches" page now uses the FML to detect when a feature configuration is invalid for the application's feature manifest. This is especially useful for deeply nested feature configurations. (erichards)