In upcoming Firefox 60, Mozilla has moved Cookies Settings into Site Data section and this change also has removed the ability to manage individual cookies in the preferences.
Cookie Settings moved to Site data section in Firefox 60
In current Firefox 58.0.2 and earlier versions, you can able to delete cookies for a site or all cookies stored on your computer by visiting options > Privacy & Security > History section (either if you choose Firefox will ‘remember history’ or ‘use Custom settings for history’).
Or you can also clear Firefox cookies by bringing up ‘clear recent history’ dialog. Let me remind you Firefox offers Forget button to clear your recent history .
Till now if you’ve deleted all cookies in Firefox, but not the individual cookies by opening Cookies dialog, the change made in Firefox 60 won’t bother you too much.
In version 60, the Firefox team has merged Cookie Settings into Site Data section, as a result the new section becomes Cookies and Site Data.
By using ‘Settings’ dialog in the new section, you can able to delete both cookies and site data, but not the cookies.
But still, by using Page info dialog (are you missing about:permissions page?) or devtools, you can able to delete individual cookies in Firefox from version 60 or later, here is how that can be done.
Clearing individual cookies in Firefox from version 60
I. 1. Click on 
button in the left of URL bar to open control center,
2. Click on ‘>’ and select ‘More information’
3. Click on ‘View Cookies’
II. For more granular control on cookies, you better visit Developer tools.
Press Ctrl+Shift+I, click on ‘Storage’ and select Cookies,
ICYDK, the Firefox version 60, offers a new preference to open search results in address bar in a new tab.
READ: Firefox 60: Always Open address bar results in a new tab
Also see: How to block Third-Party Cookies in Chrome, Firefox and IE Browsers
They have changed it since you wrote you article on how to clear individual cookies. They probably discovered the fix and changed things so that we would be prohibited from seeing and clearing individual cookies. I am beginning to hate Firefox and Mozilla! I want control over my browser, not the other way around!
They’ve not changed the things, the instructions in the article are still relevant and working, which I can confirm.
Yes, they have changed things:
https://support.mozilla.com/en-US/kb/firefox-page-info-window
“View Cookies” is now “Clear Cookies and Site Data” and it just clears all cookies and local storage for current site without giving control or ability to inspect them.
That works only for the page currently open, not any closed ones leaving cookies behind.
You have to use Dev Tools / Storage / Cookies, right click the one you want and delete.
Mozilla is the last organization I expected to engage in feature removal. You can literally still pull up the list of cookies in Manage Data, except now it is read only. You can’t edit or delete anything. So how in the hell is that “managing” data, if you can only look it? When I select the cookie and hit delete, nothing happens. Right click. Nothing. No menus in sight. It’s just stupid.
Sure these workarounds get the job done, but are horribly inefficient. You have to go visit each site individually and then open sub menus for each one. There is absolutely zero objective argument for saying that is a reasonable alternative to just scrolling down the list and deleting the few cookies you want to delete.
(v67.0.4) It appears that what they’ve done is simply removed the “Cancel” and “Save Changes” buttons from the “Manage Cookies and Site Data” dialog (though the “Remove Selected” and “Remove All” buttons remain).
You can get those buttons back by restarting Firefox in Safe Mode under Help | Restart with Add-ons Disabled…
Then you can search for and delete all the individual cookies you want and they’ll actually be deleted when you restart Firefox back into normal mode.