This extension allows typographic text processing. You just type text in any field of the browser, select «Typograf» item in a context menu and the text in the field is formatted according to typographic rules: inch signs are replaced with quotes, minus signs are substituted with dashes where it is required, etc.
Typographic processing is preformed by one of selected free services «Typograf» developed by Art. Lebedev Studio or «Typograf» developed by Eugene Spearance.
An add-on itself just takes text from the field, sends it to the selected service and puts response from the server back to the field.
You can find details about the typographing services at the sites of their authors
Art. Lebedev Studio: http://www.artlebedev.ru/tools/typograf/about/
Eugene Spearance: http://www.typograf.ru/