Ria's comment at https://bugzilla.mozilla.org/show_bug.cgi?id=366075#c4 is probably how this should work: When the pref is changed, we should immediately expire history to match it's new value. this would require: 1. ability to override partial expiration w/ specific expiration age 2. performance changes allowing bulk expiration on demand (async)

Bug 451915 - move Firefox/Places bugs to Firefox/Bookmarks and History. Remove all bugspam from this move by filtering for the string "places-to-b-and-h". In Thunderbird 3.0b, you do that as follows: Tools | Message Filters Make sure the correct account is selected. Click "New" Conditions: Body contains places-to-b-and-h Change the action to "Delete Message". Select "Manually Run" from the dropdown at the top. Click OK. Select the filter in the list, make sure "Inbox" is selected at the bottom, and click "Run Now". This should delete all the bugspam. You can then delete the filter. Gerv

no history limits anymore in FF4.0, so invalid.