Safari blocking the ubuntu.com Web site !

As I now got a 2nd laptop running windows I installed the Ubuntu Linux on it.

But as I use my MacBook for research I stumbled about the problem that access to ubuntu.com is nearly not possible using Apple Safari - the Web site loads very slow or only gives timeouts.
To check whether this is a general problem I then fired up Firefox and with Firefox on my Mac ubuntu.com loads without problems at all.

So I ask myself - why do I have timeouts or no access to ubuntu.com using latest Safari in El Capitan - but not when using Firefox ?
Is Apple blocking other Linux distributions ?