User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1a3) Gecko/20060705 BonEcho/2.0a3 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1a3) Gecko/20060705 BonEcho/2.0a3 Although the default theme shows a disabled state in its icon when the row of scrollable tabs reaches the far left end, the disabled condition is not passed to where a third-party theme can make use of it. When one uses DOMi to inspect the scrollbuttons when they are in a disabled state, the right scrollbutton shows disabled=true when one inspects it in a new window. However, when the left scrollbutton is inspected in a new window while it is in a disabled state, the disabled condition is not displayed. Although the default theme shows a disabled left arrow, when the left scrollbutton is inspected in a new window, no disabled state is present. Reproducible: Always Steps to Reproduce: 1. Build a third-party theme with the current default scrollbox.css file 2. Install it in Firefox. 3. With Firefox open, make enough tabs to require scrollbuttons. Actual Results: The left scrollbutton does not show a disabled state. The right scrollbutton does show a disabled state. Expected Results: Both scrollbuttons should show a disabled state. When scrollbox.css is transplanted unchanged from the default theme to a third party theme the disabled state does not appear. Even though the left and right codes are identical except for filenames, the right scrollbutton shows a disabled state where the left scrollbutton does not. The visual appearance is reflected in the code apparent in DOMi.

This problem turned out to be a margin issue: giving tab {} a left margin of 1px produced the results noted above. This is an invalid bug.