I have seen this happen to mail messages (threaded view) and bookmarks in my sidebar. Usually happens when I click on a message or bookmark three level nested. Here is the actual situation: Personal Toolbar Folder Mozilla Bugxilla Enter Bug When I clicked on Enter Bug bookmark on my sidebar, no page loaded on my html area. (ssme with mail. No mail message displayes in the message display) After this any click I make to the tree will cause that row to disappear. Expose will cause it redisplay correctly. After this point, no amount of clicking will get us out of this situation. I usually have to restart the app to get bookmarks to work again from my sidebar.

beta1 ing this bug

*** This bug has been marked as a duplicate of 23530 ***

marking verified, this has only been around for about a month, dp, glad you caught it :-) the bookmarks not opening when clicked is known and already filed to slamm