Well, afaict this is not actually a regression, it just didn't work from the beginning of tab-to-search implementation.
Bug 1678647 Comment 8 Edit History
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Well, afaict this is not actually a regression, it just didn't work from the beginning of tab-to-search implementation. and there are workarounds, as stated in comment 2. Search is broken if tab to search is used, but not in the other cases, right?