Since the last major upgrade of the Firefox browser (when its appearance changed) I observe that the youtube.com web page does not load properly: every day it refuses the access to it displaying the message "Hmm. We’re having trouble finding that site. We can’t connect to the server at www.youtube.com." The very same days these "no access" periods are randomly interrupted with the periods when the youtube page loads either with no problem or with empty pictures for individual videos. Nevertheless, even in the latter case the videos play after clicking them. This is the only webpage where I experience this kind of problems. All other pages on the internet seem to load properly. My children experience the same problem with the youtube page on their computer. The no-access periods do not seem to be always correlated on these two computers but I m not sure. The both computers run the Linux Mint 17.3 Rosa OS. My wife's computer that runs MS Windows does not experience this problem at all. All three computers I mentioned here access the internet via the same internet provider and the same wifi access point. The same problem experienced with the Opera and Chrome browsers when installed on this computer. The same problem occurred under the Linux Mint 18.3 OS when I booted my computer from the USB stick.