1 In the case of Sirsi (WebCat), the message "Error #csnot defined" doesn't indicate failure, but only the absence of the tested-for ISBN, 1579903002. In that case, try replacing 1579903002 with the ISBN of a book that's known to exist in your catalog in order to verify that the bookmarklet is working. Some Sirsi systems will also need cgisirsi.exe instead of cgisirsi. And some will require you to login. In other words, your mileage may vary.
2 You may need to click Search again in the popup window.
How do I find out which vendor my library uses?
Click the sample search links, and look for a familiar results screen. Or, ask your librarian!
What if my library uses a system that's not supported?
There are zillions of vendors of library software. The LibraryLookup project can add support for yours if it is possible to form a URL that queries your system by ISBN (see the sample links above). That will be true for many, but not all, systems. If you can find the magic URL pattern for your system, pass it along.