This system of transliteration is derived from the Georgian national system of romanization. Set these variables in Firefox's about:config window to use with ToCyrillic. If you can't see these characters, try loading Georgian fonts from here (just Georgian glyphs) or here (massive number of unicode glyphs). These characters are from Unicode \0x10D0 to \0x10FF, see here.

extensions.tocyrillic.layouts.georgian [["a", "ა"], ["b", "ბ"], ["g", "გ"], ["d", "დ"], ["e", "ე"], ["v", "ვ"], ["z", "ზ"], ["t", "თ"], ["i", "ი"], ["k'", "კ"], ["l", "ლ"], ["m", "მ"], ["n", "ნ"], ["o", "ო"], ["p'", "პ"], ["zh", "ჟ"], ["r", "რ"], ["s", "ს"], ["t", "ტ"], ["u", "უ"], ["p", "ფ"], ["k", "ქ"], ["gh", "ღ"], ["q'", "ყ"], ["sh", "შ"], ["ch", "ჩ"], ["ts", "ც"], ["dz", "ძ"], ["ts'", "წ"], ["ch'", "ჭ"], ["kh", "ხ"], ["j", "ჯ"], ["h", "ჰ"]]
extensions.tocyrillic.layouts.georgian.description Georgian/Kartuli (ქართული)