Unexpected changes to SearchService.sys.mjs

I noticed that between 140 and 146 we gained a strange change to SearchService.sys.mjs.

The commit ecb944a5 contains the following change:

diff --git a/toolkit/components/search/SearchService.sys.mjs b/toolkit/components/search/Searc
hService.sys.mjs
index 6240e0edf0a6..8e9fea906b95 100644
--- a/toolkit/components/search/SearchService.sys.mjs
+++ b/toolkit/components/search/SearchService.sys.mjs
@@ -2893,10 +2893,10 @@ export class SearchService {
   // called in test_remove_engine_notification_box.js
   async _fetchEngineSelectorEngines() {
     let searchEngineSelectorProperties = {
-      locale: Services.locale.appLocaleAsBCP47,
+      locale: "en-US",
       region: lazy.Region.home || "unknown",
       channel: lazy.SearchUtils.MODIFIED_APP_CHANNEL,
-      experiment: this.#lazyPrefs.experimentPrefValue,
+      experiment: this._experimentPrefValue,
       distroID: lazy.SearchUtils.distroID ?? "",
       javascriptEnabled: lazy.SecurityLevelPrefs.javascriptEnabled,
     };

Some problems:

  1. I'm not sure these changes are necessary, since our search config contains no locale information.
  2. this._experimentPrefValue does not exist as a property, and is not set. This will always be undefined. If we want this to be "", then we should set that value instead. But, similar to the previous point, I'm not sure this is necessary.
  3. If we do want these changes, they should likely should be shared with mullvad browser in the commit "BB 43525: Skip Remote Settings for search engine customization."

@pierov or @brizental do you recall why these changes were made, and why they ended up in the commit "TB 42891: Set the bundled search engine for Tor Browser."?