EDIT: Thanks for kindly replying to my review and my e-mail. Hopefully you'll be able to also fix compatibility with Firefox 27. ;)
I can only assume from the lack of communication and updates, that the developer has ceased work in this add-on. I've tried to contact him by e-mail but received no response.
Scrollbar Search Highlighter was one of the add-ons that first got me into the whole Firefox customization. This add-on provided a unique functionality, that you simply couldn't find anywhere else. Unfortunately, it fails in some specific pages and it will break completely in Firefox 27.
I have since written my own add-on, called "FindBar Tweak", which was greatly inspired by this and other add-ons. Unless work is resumed here, I would invite everyone to switch to FBT, it has a similar highlights grid in the scrollbar, with greatly improved performance and functions perfectly in frames, pdf documents, gmail, etc, and ensures it will remain compatible with future versions of Firefox!
I'm sorry for the spam, but I believe my add-on now becomes a necessary alternative to Scrollbar Search Highlighter, which will stop working completely in the very near future.