Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9b5pre) Gecko/2008031415 Minefield/3.0b5pre ID:2008031415
1) add/delete bookmark item
3) nothing change in bookmarks.postplaces.html
The bookmarks.postplaces.html file is no longer supported. It was a stopgap measure to ensure we did not overwrite bookmarks.html in the case that a user often went back and forth between Fx3 and Fx2.
As of bug 384370, we no longer write any HTML bookmarks automatically. Instead, all bookmarks (instead of just the menu and toolbar) as well as tags are backed up once every 24 hours to the bookmarks backup directory in your profile, as JSON.
If you do want to export bookmarks.html (menu and toolbar only) at shutdown, you can set this pref to true:
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.
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.