477123 - [Mac] Right-scroll button in tabbar can be mistakenly active

Status: RESOLVED DUPLICATE of bug 482965

(Firefox :: Tabbed Browser, defect)

Description

[Jeff Muizelaar [:jrmuizel]]

When I scroll through the tab bar and reach the end on the right side the tab strip right scroll button still appears active. This makes it appear as though there are more tabs. When I click on the button the tabs either don't move or move a tiny amount to the right.

It would be more helpful and consistent if the button became inactive.

Comment 1

[Steven Michaud [:smichaud] (Retired)]

This has nothing to do with 2-finger scrolling.  For some reason it
only happens on OS X, and then only on the mozilla-central and 1.9.1
branches.

Here's STR that don't require any scrolling:

1) Open just enough tabs (five or six) in a browser window for all the
   tabs to fit in the tab bar, and make the rightmost one current.

2) Slowly resize the window until the leftmost tab no longer fits in
   the tab bar.

   The right-scroll button will appear (which is correct) and will be
   active (which isn't).  When you click the button, the tabs move a
   tiny bit to the right and the button becomes inactive.

Interestingly, the "opposite" steps-to-reproduce don't work:

1) Open just enough tabs (five or six) in a browser window for all the
   tabs to fit in the tab bar, and make the leftmost one current.

2) Slowly resize the window until the rightmost tab no longer fits in
   the tab bar.

   The left-scroll button will appear and be inactive (which is
   correct).

Comment 2

[Markus Stange [:mstange]]

This bug doesn't occur when "toolkit.scrollbox.smoothScroll" is off, so it probably has something to do with the "interesting" way the scroll steps are generated in the _smoothScrollByPixels method of the scrollbox binding.
http://mxr.mozilla.org/mozilla-central/source/toolkit/content/widgets/scrollbox.xml#163

Comment 3

[Markus Stange [:mstange]]

Bug 482965 is the cause of this bug and has more information.