Last night I updated toolbar button to fix an annoying bug that was causing all the button that had drop down menus to behave wrong. It was caused my some styling I had applied to them, that caused problems in Firefox 2, but not the Firefox 3 alphas. To get the update go to Toolbar Button page.
The is also the first version to be fully compatible with the Custom Toolbar Button Maker. Previous versions had a conflict with it that caused a number of buttons (about 15) to not show up in the list of possible buttons that you could select from.