Customizable Firefox Chat Extension

I’m in need of a skilled developer who can create a custom extension for my Firefox browser. This unique tool should be capable of greeting visitors with custom messages in the chat box found on various expert websites. Here are the specifics:

- Functionality: The extension should allow each user to customize their "hi" or "welcome" message. This should not be a random or predefined message generated by the system.
- Conditions: The program should not activate itself on all pages or certain pages arbitrarily. It should instead be programmed to come alive under specific conditions that will be further discussed during the project execution phase.

Skills and Experience:
- Proficiency in Firefox extension development
- Good understanding of chat platforms
- Ability to incorporate specific triggering conditions effectively

Any developer interested in this project should have a good track record creating similar browser extensions.