By many data your browser sends to webpages you visit, webpage can create an unique ID, called simple digital fingerprint. Deleting cookies won’t help. And as for cookies, webpages can track your activity on other webs you are currently keeping in tabs in your web browser or even webpages you visited before deleting cookies. Apple introduced its Intelligent Tracking Prevention (ITP) to prevent this and Mozilla Firefox introduced similar functions too. And now, fingerprinting, since January 2020, will be blocked by default.
Since version 72, Firefox will block fingerprinting by default. If you are using Firefox 70 or later, you can already block by visiting (on macOS) “Preferences -> Privacy & Security -> Permissions -> Prevent accessibility services from accessing your browser” or (on Windows) in Firefox’s settings by visiting “Options -> Privacy & Security -> Permissions -> Prevent accessibility services from accessing your browser”. Mozilla offers this feature since version 41 from year 2015, but I can’t provide infos about where exactly is this feature “hidden”. Way written above applies to version 70 (or later) and it’s possible that versions older, but close to 70 may have very similar or the same path where to enable blocking fingerprinting.
Someone may ask, what if some webpages will detect that they are getting minimum datas from you and will block you from accessing website, something similar like do some webpages when you are blocking ads?
Just download browser extension, which will serve dynamic false data. There are already such extensions. Solved.
I understand that many indie webs need to serve ads to get paid their bills. Personally, if ads are not over whole webpage and do not distract me, I have no problem to whitelist such websites and sometimes to click some ads. Clicking on ad you hate is also great way how to fight with ads – you will support your favorite web page and ad companies will get nothing. Another situation is aggressive tracking often abused to read what are you doing on web. This is unacceptable. Webs like Google and Facebook are excessively spying on your Internet activity and it’s only good to see that some browsers, like Mozilla Firefox or Apple Safari, are fighting this. Privacy issues were also reason why I had as my secondary browser replaced Google Chrome with Mozilla Firefox.