Modify Header Value
Add, modify or remove a header for any request on desired domains.
Modify Header Value: Firefox Add-on for HTTP Requests
"Modify Header Value" is a Firefox extension designed for app developers, website designers, and testers who wish to modify HTTP-request-headers. This extension enables users to easily add, change, or remove an HTTP-request-header for every request on the desired domains or URLs. One can deactivate or activate the add-on or individual header items with a simple toolbar icon click. The extension comes with an options page for the adjustment of each header item and an illustrative example on adding custom headers.
Add-on stats
Weekly download count: 485
Firefox on Android: Yes
Risk impact: High risk impact 
Risk likelihood:
Manifest version: 2
Permissions:
- storage
- <all_urls>
- webRequest
- webRequestBlocking
Size: 105.42K
Email: mi*****@yandex.com
URLs: Website
Ranking
# 717 ▲ 21
Other platforms
Not available on Android
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Add-on summary
Modify Header Value can add, modify or remove an HTTP-request-header for all requests on a desired website or URL. This Firefox add-on is very useful if you are an App developer, website designer, or if you want to test a particular header for a request on a website.
Key features:
- Easily add, modify or remove a header for any request on a desired domain(s).
- For a complete list of HTTP headers, please take a look at the list of HTTP Header Fields in Wikipedia.
- Clicking on the Toolbar icon allows you to disable or enable the addon.
- Each header item has several options to adjust (see add-on's Options page for details)
- You can add several header items and active or inactive them separately.
- An example in the options page shows a tutorial on "How to add a custom header".
Note: to report bugs, please visit add-on's homepage and fill the bug report form.
Review on YouTube: https://www.youtube.com/watch?v=KM4uKx-BjIg
User reviews
These summaries are automatically generated weekly using AI based on recent user reviews.
Firefox Browser Add-ons does not verify user reviews, so some user reviews may be inaccurate,
spammy, or outdated. Pros
- Useful for modifying headers for specific use cases
- Works in private mode, which is appreciated by users
- Allows users to tweak any desired header
- No bugs or issues experienced by multiple users
Cons
- Extension breaks YouTube when changing the 'User-Agent' header
- Difficulty working around CORS protection
- Lacks option to edit response headers
- User interface needs refinement
Most mentioned
- Breaks YouTube with 'User-Agent' changes
- Need for editing response headers
- Works well in private mode
- Desire for export/import feature for rules
User reviews
Was alternatively using requestly to handle this specific use case, but with the direction they've been going this has been a really nice alternative
by Firefox user 18776916, 2025-01-11
As Security Researcher, I've found this add-on very useful.
I never even had any bug or issue.
Absolutely 5 stars!! <3 💯 ❤️
by Good Vibes, 2024-10-19
Extension now breaks youtube if you change the "User-Agent" header just to make people aware
never did this previously so either something changed with the extension or youtube changed something
by Firefox user 17327488, 2024-08-10
Add-on safety
Risk impact
Modify Header Value requires some sensitive permissions that could impact your browser and data security. Exercise caution before installing.
Risk likelihood
Modify Header Value has earned a fairly good reputation and likely can be trusted.
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