How do ad blockers work?

Related questions

1. Does Adblock work on Firefox?
2. Does AdBlock slow down Firefox?
3. Is Adblock for Firefox free?
4. Is there AdBlock for Firefox?
5. Does Firefox Mobile block ads?
6. What is uBlock on Firefox?
7. Does Adguard cost money?
8. Where is the ad blocker on Firefox?
9. Is there a free version of AdGuard?
10. Is Adguard for Windows free?

Tags

1. #instead
2. #blockers
3. #filter
4. #allow
5. #appear
6. #every
7. #relies
8. #sites
9. #pages
10. #injects
11. #whitelisted
12. #blocked
13. #means
14. #block
15. #adblock
16. #called
17. #rules
18. #visit
19. #stylesheet