Here’s a refined version of your job post for the browser extension modification:
Position Overview:

We are seeking a developer experienced with Firefox extensions to help us modify 24 custom language extensions for our forked version of the Firefox browser. The primary task is replacing all instances of "Firefox" with our browser’s new name. Additionally, we will require your advice and support in ensuring that the browser only accepts these custom extensions by modifying plugin ID codes.

This project will be milestone-based, with the first milestone being the modification of one extension (XPI). Upon successful completion, additional milestones or bonuses will be provided for each of the 23 remaining extensions.
Key Responsibilities:

    Modify Language Extensions:
        Replace all instances of "Firefox" with our browser’s new name in the provided language extensions (.XPI format).
    Browser Modifications:
        Modify our custom web browser to only accept the modified language extensions by changing plugin ID codes.
    Consultation:
        Provide advice and guidance to ensure the extensions work seamlessly with our custom web browser.

Requirements:

    Experience with Firefox Extensions:
        Strong understanding of how to modify Firefox extensions (.XPI).

    Browser Modification Experience:
        Experience working with or modifying browser forks, particularly those based on Firefox.

    Attention to Detail:
        Ability to ensure consistent branding changes and functionality across all extensions.

Compensation:

    The initial milestone will cover modifying the first extension.
    After successful completion, we will proceed with setting additional milestones or paying bonuses for each subsequent extension.

How to Apply:

Please provide details of your experience with Firefox extensions, and any relevant examples of similar projects. We look forward to working with a developer who can efficiently modify and integrate our custom language extensions.

Let me know if this aligns with your expectations!