Rated 2 out of 5 stars

Says Not Found but brings you to their website where you can then input information. Brings back results with some pdf's but also link to books only.

Rated 1 out of 5 stars

I did the unfortunate mistake of adding Ebook PDF search engine's add-on to SeaMonkey and now there's no way of getting rid of it. Not even re-installing SeaMonkey etc. helped.
First time used it set itself in the main search and url bar as search engine, which cannot be changed anymore.
The whole browser became useless because of it.

Rated 5 out of 5 stars

I've always found openpdf.com to be a very useful resource. It is a search engine for PDF documents (eBooks) which also has a built in PDF viewer, allowing the viewing of them directly from the site. They can also be viewed in a PDF viewer (Adobe Acrobat, Evince etc.). This Firefox add-on makes openpdf.com even more convenient to use, as it facilitates the searching for PDF document directly from the Firefox search box. If you need a PDF search engine, then I can highly recommend this Firefox add-on.

This review is for a previous version of the add-on (20100502).