Okay, problem solved. Bear with me as I share my little venture!
I occasionally get this with ads, possibly adblock is taking a while to block the ads. What happens if you hit refresh while it's hanging?
Refresh button has no effect.
I do not use the adblock extension, but to block most ads I use a secondary hosts file with dnsmasq and a similar file with squid. I temporarily disabled the dnsmasq and squid services. I temporarily configured firefox not to use any proxies.
Same hanging result.
However, the progress bar finally completed after about 3.5 minutes. Perhaps this was happening before but I lacked the patience to wait that long.
I kept dnsmasq and squid disabled. I restarted Firefox in safe mode (I have the NoScript extension installed and there are too many associated options that could affect what I am seeing.).
Same hanging result.
However, the idea of ad blocking reminded me that the hanging effect often is related to DNS lookup issues. Hmm.
I maintain in my /etc/hosts file the IP addresses of all the sites listed in my Firefox bookmarks. This was a habit I started long, long ago when I was miserably stuck on dial-up. Every little tweak helped in those days. I ran a daily script through cron to keep the hosts file fresh. I still run that daily script because, well, every little tweak helps. Still . . . I wondered.
I keep a /etc/hosts.min file that contains nothing but the bare minimum for my modest home network (I use static addresses). I renamed /etc/hosts to hosts.bak and copied hosts.min to hosts.
I started Firefox in safe mode and tried the slacky.eu site. The progress bar completed in <drum roll> --- less than 4 seconds. Actually, the page loaded completely immediately --- the time delay is probably caused by the site being on the opposite side of the world from my location and possibly a slow or busy server.
Next I started Firefox in normal mode. Same pleasurable non-hanging result.
Next I restarted both squid and dnsmasq. I restarted Firefox in normal mode. Same non-hanging result.
I restored my original /etc/hosts file. Same hanging result.
Okay, now my curiosity is peaked. Which IP address in my hosts file is the cause?
I opened the source code for the slacky.eu web page and scrolled through http URLs and matched any I found in my original /etc/hosts file. I found only one suspect. I commented out the reference and restored my original hosts file.
I started Firefox in normal mode. Same pleasurable non-hanging result.
I used dig to find the IP address for the problem URL. Nope, not the same as what was in my hosts file. I edited the IP address in my hosts file. I restarted Firefox.
Problem solved. No hanging.
Oh, I suppose you want to know the culprit URL, huh?
<Playing Alfred Hitchcock suspense movie organ music in background>
This hanging issue has been occurring for a long time. Therefore I have no idea why my daily updating script is installing the incorrect IP address for www.paypal.com
. I'll have to look into that.
I hope you enjoyed the little story. Thanks for helping!