User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.5a) Gecko/20030718 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.5a) Gecko/20030718 First create a tabbed bookmark (3 sites and 12 sites in my case) Close down and restart Mozilla Go to http://www.slashdot.org Open any tabbed bookmark. Press the Back button and all of the tabbed Windows disappear. Go forward and the tabs come back. If you open another group of tabbed bookmarks, the current tabs close down and open only the new tabs. Some new preference setting I missed maybe? Reproducible: Always Steps to Reproduce: 1.First create a tabbed bookmark (3 sites and 12 sites in my case) Close down and restart Mozilla Go to http://www.slashdot.org Open any tabbed bookmark. Press the Back button and all of the tabbed Windows disappear. Go forward and the tabs come back. If you open another group of tabbed bookmarks, the current tabs close down and open only the new tabs. 2. 3. Expected Results: Back button should only affect the current tabbed window, not the entire broswer session.

Only tested on Mozilla Version 1.5a

I think that this is by design

This was introduced with Bug 203960 Make bookmark groups conditionally replace existing tabs instead of appending The 'conditionally' got forgotten, this 'fix' replaces all existing tabs, so that behaviour of the Back-Button prevents some, not all, dataloss introduced by this 'fix'. The Back Button doesn´t always work correctly.

Now there's a preference to select the behaviour. *** This bug has been marked as a duplicate of 203960 ***