I’m running OpenSuse 42.2 KDE Plasma 5.8.6 kernel 4.474-18.2-default.
My browser is Firefox ESR 52.2.0 and using add-ons uBlock Origin' and Self Destructing Cookies’.
I suspect that some of the cookies allowed on my system (thanks to S.D.C.) are tracking my browsing activities.
How can I find out which may be guilty?
IMHO you can’t. Cookies are just cookies. You can only suspect cookies of containing information that is used for tracking.
But one of the things you can do (I have limited knowledge about this) is restricting sites by setting that all their cookies will be made “session only” (I except only a few trusted sites, like by bank, from this). Then at least when you finish using the browser (and that assumes that you do that from time to time, either by closing all windows of a browser or automatically when you shutdown your system in the evening) all those cookies will be deleted.
And of course checking regularly which cookies are stored and eventually cleaning up is also a good action.
Thanks for your input!
I’m using the Self Destructing Cookies add-on to ensure that almost all cookies are treated as `session only’.
I decided to do some digging in the FireFox add-ons and found BitDefender TrafficLight…
It’s able to indicate those web sites that DO have active trackers associated with them.
Once its installed, when you Left Click on TrafficLight’s icon (green tick) a small window then provides information about the site.
Probably the more precise answer is that it’s usually not anything in the cookie content although for specific purposes something can be in there.
Tracking has more to do with <how> specific cookies are used, it’s the practice of when visiting a website, a particular cookie is placed on your machine, then when you visit another site which might have something in common with the previous site (eg the same advertising company), the cookie from the previous site is read into the new site… and so on for every website you visit.
Ordinarily, a User might expect that a cookie might be used only for the one site visited, but some companies have interests across many websites and want to know as much as possible about your previous visits to other sites and find it useful to use cookies to identify you (generally as a generic somebody, not actually by name or other personal information although cross-checking data can easily identify you personally).
So, anti-tracking software generally create a list of these companies that use cookies this way and offer to delete their cookies.
HTH,
TSU
As the OP is using firefox…
paranoia
don’t forget the “supercookies” (dom.storage) that may be lurking in:
~/.mozilla/[path to your profile]/storage/*
~/.mozilla/[path to your profile]/webappsstore.sqlite
/paranoia
You can of course disable dom.storage by setting dom.storage.enabled to false (about:config) but then some sites may not work… 
Flux, thanks for your excellent response. Appreciate your explanation!
Thanks for reminding me! I had recently been looking at this possibility, so you can guess what I’m about to do next :shame:
If you are interested…
Quite a lot of firefox related related security and privacy information can be found on the “ghacks” website.
Take a look here for starters: https://www.ghacks.net/overview-firefox-aboutconfig-security-privacy-preferences/
I’ve also been using the following web browser built on FF,
It has a number of anti-tracking and anti-spam built in.
TSU