wow, tnx for advises, guys
Addons for Firefox is great, but I use it only for dowload Opera and chrome. IMHO FF in comparison with Opera&Chrome is very slow.
usually i dont use FF for normal browsing... i prefer lighter browsers as epiphany...
but FF has great extensions as PDFit and downloadhelper....
i use downloadhelper for downloading videos from youtube and such places...
it also has a nice feature of converting the videos to the extension u want as .avi or .mp4
you can try it...its nice