Between ESR 115 and ESR 128, upstream completely refactored their search engine configuration. As a result, they decided engine IDs could use dash only for the locale, and added a list of exceptions for legacy engines that already had a dash in their name (`NON_SPLIT_ENGINE_IDS` in `toolkit/components/search/SearchService.sys.mjs`). In Firefox 131, they removed that list (568c4b44b9e6659b01b628c905a759e07850d21e). We should investigate if this has consequences for us (for `ddg-onion` and `startpage-onion`). In addition to that, that commit also refactors the rest of `_fetchEngineSelectorEngines`. Notice that search engine webextensions have been removed with Bug 1885953 in Firefox 135 (#43111). The commit in 130 before all this mess was 5613de84569bf.