Hi, current version is 61.0.1

Tamper Data is for 56 and below and it has not been updated in 8yrs so would be considered a security issue.

These would possibly do something of the same: https://addons.mozilla.org/en-US/firefox/addon/modify-header-value/

So wanting to hack I gather, you will have to find what else you need your self.

we try to firefox virsion 48 bt also there was arror :Not compatible with Firefox 48.0 please guide me how to add it to browser and you also we download http modify header bt there not show any tollbar this icon

HI, Mozilla only ok's Developers Extensions for use with Firefox and supplies them with a web page for distribution : https://addons.mozilla.org/en-US/firefox/addon/modify-header-value/ The Developers page has info about running the program in point form. If you need further help contact the Developer from the Links on the web page. Firefox Support only helps if it is breaking Firefox and this is not the case.

As I stated before the Extension has not been updated in 8yrs and is thus abandoned and there is no Support for it. https://addons.mozilla.org/en-US/firefox/addon/tamper-data/ Sorry, if it does not work, it does not work.