I think it would be a great idee to keep the surf history, bookmarks, entered search requests and anything else forever, not delete it automatically, neither really delete it by user action when deleting history in Firefox GUI, but to keep all the data it in a separate file in firefox folder, which is never deleted.
It can be a valuable source for statistics and data for e.g. surf suggestions, auto complete and input suggesstions for awesome bar and much more, if not as basic feature of firefox then maybe it could be used by 3rd party plugins.
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