Firefox Extension and Chrome Extension that replace Code

Avg Bid (USD)
Project Budget (USD)
$100 - $200

Project Description:
I need a chrome extension and a firefox extension both will need permissions to access all data on all websites the user visits.
The extensions will replace an a specific java script

if the website visited by user contains

then the extension will replace the script above to the following:

The original javascript ([url removed, login to view]) will never be executed and the new javascript will be properly executed as if the webpage contained it from the beginning.

The original javascript could change in some lines.
So I need several ifs (something around 15) if the original javascript has specific text on it.

I need to replace the javascript on each case for codes that I will give you.

Those codes needs to be loaded from an external file on my site. So that way I can change the codes whenever I like. (I accept suggestions on this feature, auto-update maybe could work [url removed, login to view] )

finally the extension needs to load an specific url, just 1 time (could be a 24 hours cookie) and into background. This will be only if the user is visiting my site.

Additional Project Description:
03/27/2013 at 9:52 AKDT
code.txt is the original javascript.

Please see the attached file

Skills required:
Firefox, Google Chrome, Javascript
Additional Files: code.txt
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