[Kiyo]

With the new version of Firefox, Tamper Data is no longer compatible. I've looked at many tutorials and still have yet to come to a conclusion on how to install it. If anyone could help me, I would greatly appreciate it and throw you a few dollars.

Please get back to me as soon as possible. Thanks

[CyberStrike]

I use Firefox 52 ESR, but I personally also use burp or zap. You can use owasp mantra or waterfox as well, that is an option. If you want try

https://www.askvg.com/how-to-fix-broken-...w-version/

[Kiyo]

I use Firefox 52 ESR, but I personally also use burp or zap.  You can use owasp mantra or waterfox as well, that is an option.  If you want try

https://www.askvg.com/how-to-fix-broken-...w-version/

When I click that link, it just says Denied.

[Soledge]

Try burpsuite it’s an intercepting proxy that does the same thing as tamper data

[r3el]

use brup suite . if you need help with it i can help u
or use Firefox 56.0 it works for me now
find 56.0 here >> ftp.mozilla.org/pub/firefox/releases/56.0/

[CyberStrike]

When I click that link, it just says Denied.

arg I got the same thing but searching it on google it went through I wonder if it blocks the referer ... I googled " tamper data firefox 60 " minus the quotes it was 5th link down . so odd

How to Install Incompatible (Unsupported) Extensions in Mozilla Firefox Newer Versions?

So you installed a new version of Firefox or installed an update and now your favorite extension is no longer working. It has been disabled by Firefox. Do you want to re-enable your favorite extension or want to install an incompatible extension in Firefox?

Don't worry! You have come to the right place. This tutorial will help you in making your favorite extensions compatible with Mozilla Firefox and will also help you in installing incompatible extensions.

Many times a few already installed extensions are automatically disabled after updating Firefox version or you can't install a new extension because its not compatible with Firefox version. It happens because the developer didn't update the extension or the developer failed to code the extension compatibility version properly.

Anyway there are a few possible methods, which can be used to make any extension working in Firefox even if it was disabled because of the compatibility issues:

Using Nightly Tester Tools extension
Using Add-on Compatibility Reporter extension
Using Firefox built-in about:config tool

UPDATE: New Method to Install Incompatible (Legacy) Extensions

The newer Firefox versions come with all legacy add-ons disabled by default. Now Firefox only supports WebExtensions.
If you want to enable support for legacy extensions again, set the "extensions.legacy.enabled" preference to true in about:config page. Now all legacy extensions will start working again in Firefox.

A. Using Nightly Tester Tools Extension:

"Nightly Tester Tools" is a great extension for Mozilla Firefox which can help you in installing an incompatible extension or enabling an already disabled extension.
You can download it from following link:

Download Nightly Tester Tools

It also provides many other useful features like:

Customize Firefox titlebar text
Copy build tag to clipboard
Copy list of installed extensions to clipboard
Open profile folder
Take screenshot

B. Using Add-on Compatibility Reporter Extension:

Add-on Compatibility Reporter is an official Mozilla Firefox extension developed by Mozilla itself which automatically enables incompatible extensions and let you report them to Mozilla.

This extension allows you to test whether your favorite extensions still work with the version of Firefox that you're using. If you notice that one of your add-ons doesn't seem to be working the same way it did in previous versions of the application, just open the Add-ons Manager and click Compatibility next to that add-on to send a report to Mozilla.
You can download and install it using following link:

Download Add-on Compatibility Reporter

Thanks to our readers "Archy" and "carbonize" for mentioning it...

C. Using Firefox built-in about:config Tool:

1. Type about:config in Firefox addressbar and press Enter. It'll confirm, click on I'll be careful, I promise! button.
2. Now right-click and select "New -> Boolean". Set its name in following format:

extensions.checkCompatibility.version_number

For example, if you are using Firefox 10.0, you'll need to set the name to extensions.checkCompatibility.10.0 and if you are using Firefox 11.0 beta, you'll need to set the name to extensions.checkCompatibility.11.0b. Similarly if you are using Firefox 12.0 alpha, you'll need to set the name to extensions.checkCompatibility.12.0a and so on.

Now set value of this new boolean key to false.

3. Again right-click and select "New -> Boolean". Give it name extensions.checkUpdateSecurity and set its value to false.

4. That's it. You have done. Restart your browser and now all disabled extensions will be enabled and you'll be able to install new incompatible extensions as well.

NOTE: You can also change value of extensions.lastAppVersion to the version no which is compatible with your favorite extension. After installing the extension, you can revert back the value. It'll not affect the installed extension.

BONUS TIP: There is another method to modify .rdf file of the extension and change the maxversion value to make the extension compatible. But its a complicated method and is not required or recommended when we have the above mentioned easy methods.

There are a few pictures as well for setting it up. I apologize about that.

[Gee4rce]

An alternate to the above named interception proxies is Teleriks "Fiddler",
i use it a lot and it's doing a pretty good job. For Chrome atleast a mate wrote a LiveHTTP equivalent:
https://hackforums.net/showthread.php?tid=5809235
Cheers, Gee.