My addon "XUL/Migemo" https://addons.mozilla.org/en-US/firefox/addon/xulmigemo/ provided ability to search history/bookmark/tabs from the location bar, with custom search conditions based on regular expressions. In other words, it applies custom filter for search results of unifiedcomplete. After XUL is ended, we need something to do it. The addon replaces the component to provide searc hresults for "unifiedcomplete" autocomplete, with monky-patched version. https://github.com/piroor/xulmigemo/blob/master/components/UnifiedCompleteOverride.js The difference of the original version is: if lists all history entries (or tabs) from the Places DB, but filter them with custom condition based on a given regular expression generated from the user input. As the result, the addon provides ability to find webpages from bookmarks or histories ignoring difference of phonetic modifiers (like accents). This is similar to bugs about omnibox API (tracked at the bug 1166831), but I think they have different purposes for each. The omnibox API allows people to provide extra custom suggestion items but doesn't allow to replace default results. On the other hand, this planned API provides ability to custom default search results.
Oops, there is a fatal typo... > if lists all history entries *it* lists all history entries
If 1) the omnibox API provides ability to replace all results completely, and 2) if we can get search results from all histories and bookmarks like regular search results sorted by their "frequency" via other already-planned APIs, then, I think this proposal can be unnecessary and closed as duplicated.