dns cache problem

Hello the family ;) It's me again, I have a person who told me about a dns cache problem, or something like that, in short, I have indeed since noticed that well after closing the Firefox browser, requests continue on the sites that I visited and that long after my last connection. What about, bug or not? https://translate.google.fr/translate?hl=&sl=ru&tl=en&u=https%3A%2F%2Fwww.linux.org.ru%2Fforum%2Fgeneral%2F15622136&sandbox=1 the link speaks about it too. Cordialy.