HTTP Header Mangler od Peter Nilsson

HTTP Header Mangler is a Firefox add-on which inserts HTTP headers on a per host basis.

Matching of hosts is done with either simple strings or regular expressions.

Rules can have multiple headers apply to multiple hosts, or simply insert a single header for a single host.

Example rules:
example​.com
.*regexp\d+
# This is a comment.
X-Forwarded-For=10.11.12.13

# Delete headers using "" or ''.
X-Forwarded-For=""
X-Forwarded-For=''

    # Indentation is allowed.
    foobar
# Formatting with whitespace is allowed.
X-Forwarded-For    =    100.101.102.103
User-Agent         =    Mozilla/3.0 (X11; I; AIX 2)

# Here's an incomplete rule, which will be ignored.
Accept-Language=en-US,en;q=0.5

Thanks to https://github.com/aexaey for the contribution.

For more information, please visit HTTP Header Mangler on Github.