After upgrading from stable to testing firefox started having the
mentioned problem again.
"firefox --version" gives me "Mozilla Firefox 50.1.0", apt tells me it
"uname -a" gives "Linux toothless 4.11.0-1-amd64 #1 SMP Debian 4.11.6-1
(2017-06-19) x86_64 GNU/Linux"
The problem does not appear with firefox-esr=45.9.0esr-1 (amd64)
The problem affects the following websites:
It does not affect: