Combining the power of Firefox, Google and the Mechon Mamre text library, this extension allows you to search the Hebrew texts of Tana"ch, Mishna, Talmud Bavli, Talmud Yerushalmi, Tosefta and Mishna Torah. You can search as broadly as all of these sources or as specifically as a single book of Tana"ch, a single tractate of Mishna or a single set of Halachot of the Mishnah Torah. The extension includes an onscreen Hebrew keyboard to assist those who do not know the Hebrew keyboard layout and/or do not have Hebrew input support on their machines. (You can use this keyboard to copy and paste Hebrew text into other things also).
This is still in development. There are many more features to come, including morphological search, search term highlighting and find in page. Let me know if you have any other suggestions.