Description of Problem:
If the bookmarks tab is removed (any tab, I guess) from "My Sidebar" it
cannot be added back.

Version-Release number of selected component (if applicable):
mozilla-0.9.2.1

How Reproducible:
Always.

Steps to Reproduce:
1. Open "My Sidebar"
2. Pick "Tabs > Customize Sidebar ..."
3. Remove "Bookmarks"

Actual Results:
The tab is removed, but there is no way to add it back.

Expected Results:
It should appear on the left hand side so that I could add it back.

Additional Information:

My real problem was with bookmarks from an existing installation of mozilla
not showing up. Some search on http://bugzilla.mozilla.org turned up
bug #71685, but attempting the workaround described there (remove bookmarks
tab then add it back) led me into the above described scenario.

In case it helps someone, bug #71685 suggests also a different solution
which worked fine for me: hand edit panels.rdf under the ~/.mozilla tree
and replace "bookmarksPanel.xul" with "bm-panel.xul".