Ah. No :-(
I see a blank page with only a red rectangle in the middle of the screen, which is generated by ESET, saying what I wrote in my inital post., i.e., connection terminated, access denied, etc., and which threat was detected (" JS/Redirector.NAV Trojan"). See attached screenshot.
Furthermore, it is blocked not only for the browser but also for other programs. There is a repository for R, CRAN, accessible via cran.r-project.org, from which e.g. the R console and the R IDE "RStudio" can install new packages. These programs cannot access the repository as well.
Concluding, I can not visit the site and I cannot access the package repository. I wonder why it doesn't work on my PCs (2 systems, both having Smart Security 9 installed) but works on other systems (e.g. your system).
Greetings and thanks.