Thank you for looking into it.
Yes, I'm using Adblock Plus (on Firefox 50 running under macOS).
This morning, I clicked on the Log-In link on the main page and it redirected to that pesky fake Flash installer:
http://cdn.freelob.com/lp/?btp_h=516003 ... ayer-npapi
After that I clicked on various links on the site and it did not happen again.
But yesterday and after posting my previous message, I had several cases of clicking a site link on the main page ("forum", "about us") redirecting to downloading different malware dmg than the Flash oe mentionned above. I was redirected to MacKeeper or something and I've even seen (only once) the register link redirecting to register to another movie related site !!!.
This is very intermittent so after these redirects happens it may not happen for a while. But it will happen sooner or later eventually.
I turned of Adblock and will see how it goes. Not sure this is macOS specific but the download I got sure are mac specific.