Rated 5 out of 5 stars
This add-on is so convenient and time saving I found it hard moving to unsupported versions of TB/FF. Until I found a fix :)
I noticed a comment from the dev saying Mozilla only allow one button per extension. There is a 'Custom Toolbar Button Maker' on his website, so I thought I'd try creating an extension with just one button. Sure enough, it worked. The button was added to the customize box. It means making a new extension for each button, but they're so quick to make and install you may be able to have this entire extension working again (haven't tried every button). Most of us only want a handful of buttons anyway, so it takes no time at all.
Hope that helps fellow frustrated toolbar buttons users :)