Problems with websites not reachable

Most likely, since one of the last upgrades of Tumbleweed, I am having problems connecting with several websites. All opensuse.org websites {forums,downloads,www}, to mention a number are unreachable. They give a timeout in Firefox. When I try to connect from my telephone with Firefox to one of these sites, I get a connection. Also when I use Leap 15.3 the connection gets established. I can connect to other websites, but also other websites are unreachable. Anyone else having this problem? Could it be an IPv6 problem? -- fr.gr. member openSUSE Freek de Kruijf