What format to convert videos to using download helper and converter helper. On firefox for an iPod nano 5g ?

MP4 format is recommended. Here this iPod video converter may help you to solve the problem: http://www.dvd2ipad.net/ipod-video-converter.html

MP4,I recommond Aunsoft Video Converter,and there's also version for MAC.This tools has a lot of output settings,such as IPOD ,PSP,IPHONE,YOUTUBE,it's very easy to use and convert at fast speed.have a try

mpeg4

and I recommend Tenorshare Video Converter for you

Tenorshare Video Converter is a superior video converter for iPod that can convert video files/movies to iPod Video and the latest iPod nano, iPod touch and iPod classic. Tenorshare Video Converter can perfectly convert almost all popular video and audio formats to iPod MP4 and MP3, such as convert AVI to iPod, MPEG to iPod, WMV to iPod, MOV to iPod, MP4 to iPod, RM to iPod, RMVB to iPod, DivX to iPod, ASF to iPod, VOB to iPod, 3GP to iPod.

You can try top5soft youtube video converter, it is the best

hi dear

you can try use Nidesoft total video coverter

i used it which work very good for me

it support all popular video format

hope it's will help you

you can free download and try use it from this link

http://www.nidesoft.com/total-video-converter.html