User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7) Gecko/20040616 Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7) Gecko/20040616 A user that isn't interested in the sidebar feature will most likely close it by dragging the border all the way to the left, changing the size of the sidebar to zero. If at some later point, the user hits Alt-PageUp by mistake, the sidebar will pop open slightly, typically the width of three characters (I just measured it and it and it was 30 pixels). Evidentally, the intended behavior of Alt-PageUp is for it to do an implicit "F9", and return the sidebar to the original width before it was closed. In this case, it is not correctly "restoring" that width: when the width is zero, Alt-PageUp should do nothing. Having Alt-PageUp open the sidebar at all in these circumstances seems dubious to me, but having it open only 30 pixels is just a gratuitous annoyance. It's useless by anyone's standard. Not incidentally: it took me a *long* time to figure out that a mistaken Alt-PageUp was what was causing the sidebar to pop out like this. It gave me the impression that there must be some sort of keyboard method of moving the sidebar border around, and every so often I would go looking for it by trial and error (alt-ctrl-pageup? alt-shift-pageup? alt-ctrl-leftarrow?). I didn't learn about F9 until doing research to report this as a bug. Reproducible: Always Steps to Reproduce: 1. Drag sidebar border all the way to the left. 2. hit Alt-PageUp Actual Results: The sidebar border pops out 30 pixels. Expected Results: Nothing. If you've set the sidebar to a zero size, it should stay a zero size An older discussion of this issue: http://bugzilla.mozilla.org/show_bug.cgi?id=252502 There may be some connection to this but: http://bugzilla.mozilla.org/show_bug.cgi?id=252524 (I'm about to attach a png that confirms that behavior, as well as demonstrating the bug I'm reporting).

Also note that the sidebar is essentially empty. If I punch "F9" to close it, and then punch "F9" again, the sidebar shows the usual contents (or 30 pixels worth of it anyway).

*** Bug 252502 has been marked as a duplicate of this bug. ***

And again: bug 252524 may be related

Similar issue in bug 126968

Then again.. it's possibly by design? bug 29573

Confirming based on dupe.

*** Bug 126968 has been marked as a duplicate of this bug. ***

Well, apparently it's by design: bug 29573, which is VERIFIED FIXED, sets a minimum width for the sidebar. Here's what I observe: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.2pre) Gecko/2008071201 SeaMonkey/2.0a1pre F9 toggles the sidebar open/closed; Alt+PgUp and Alt+PgDn both open the sidebar, in addition they flip up or down to the next sidebar tab. Whenever one of these keystrokes "open" the sidebar, if the latter was previously "dragged to 0px" it gets slightly open, let's say one centimeter or slightly less. Since the "minimum sidebar width" is by design, this behaviour is "not a bug but a feature" => INVALID.