Preethi Issac

## Steps to reproduce Both of the iOS products report search.default_engine metrics, currently documented in the same manner: > The default search engine identifier if the search engine is pre-loaded...

adding new incident regarding Spike in the [search_engine_changed probe](https://dictionary.telemetry.mozilla.org/apps/firefox_desktop/metrics/search_engine_default_changed) for users who had an engine update for versions >= 124

Incident note: Spike in the search engine changed probe

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add another data incident regarding Spike in the [search_engine_changed probe](https://dictionary.telemetry.mozilla.org/apps/firefox_desktop/metrics/search_engine_default_changed)

Incident note: Spike in clients with null default search engine

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Adding update regarding the data incident of seeing null values for default search engines for Firefox iOS