following link helped me a lot.
https://developer.mozilla.org/En/Firefox_addons_developer_guide/Let%27s_build_a_Firefox_extension

1. start / create with new profile "dev"

"%ProgramFiles%\Mozilla Firefox\firefox.exe" -no-remote -P dev

about:config
javascript.options.showInConsole     true
javascript.options.strict     true

installed Chomebug and Dom inspector add-ons

My Extention folder for dev profile is:

C:\Documents and Settings\jobin_augustine\Application Data\Mozilla\Firefox\Profiles\jnajrasi.dev\extensions


created a text file jobin@abcd.com in C:\Documents and Settings\jobin_augustine\Application Data\Mozilla\Firefox\Profiles\uem10duz.default\extensions
(attaching the file) with only one line of text:  C:\Docs\Dell\HCheck\


For Chrome Extension: Please read:
http://www.linuxuser.co.uk/tutorials/develop-for-google-chrome-making-apps-and-extensions/3/