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ImTranslator provides translation powered by Google Translate, Microsoft, Babylon for 70+ languages. It includes Translator, Dictionary, Text-to-Speech, Back Translation.
Video Tutorial: http://youtu.be/qyLyFkQuMGU
With EPUBReader you can read ePub files just in Firefox. No additional software needed!
Translate the whole entire page or just a selection using Google Translate.
— Open web pages saved with Internet Explorer or other browsers (MHT)
— Save many tabs, video and audio reliably, in a single ZIP file (MAFF)
— Return to the original site you saved a page from, and more!
UnMHT allows you to view MHT (MHTML) web archive format files, and save complete web pages, including text and graphics, into a single MHT file in Firefox/SeaMonkey.
FontFinder is created for designers, developers and typographers. It allows a user to analyze the font information of any element on a page, copy any piece(s) of that information to the clipboard, and perform inline replacements to test new layouts.
This add-on lets you print a webpage's area easily.
Never lose anything you type into a web form again! Lazarus securely auto-saves all forms as you type, so after a crash, server timeout, or whatever, you can go back to the form, right click, "recover form", and breathe a sigh of relief.
Russian spellchecking dictionary
Saves highlighted text to a file in the specified directory
Multi-Translator from Google, Bing and Pragma.
Translation tool for your Firefox and Thunderbird with a simple and friendly interface.