Intermittent Server Not Found

[Rex]

Intermittently while browsing old and new sites, I run into a Server Not Found, "Hmm. We’re having trouble finding that site.", "We can’t connect to the server" page. To workaround I will often hold down the enter key to rapidly re-attempt to get to the page or close the tab, try again, and repeat until I get through.

Running in a new Firefox profile and in safe mode seems to make no difference.

I am running the Firefox beta from the PPA (62.0b20) on my Linux Mint 18.3.

apt-cache policy firefox
firefox:
  Installed: 62.0~b20+build1-0ubuntu0.16.04.1
  Candidate: 62.0+linuxmint4+sylvia
  Version table:
     62.0+linuxmint4+sylvia 700
        700 http://packages.linuxmint.com sylvia/upstream amd64 Packages
     62.0+build2-0ubuntu0.16.04.4 500
        500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
 *** 62.0~b20+build1-0ubuntu0.16.04.1 500
        500 http://ppa.launchpad.net/mozillateam/firefox-next/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status
     45.0.2+build1-0ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages

[Paul White (paulw2u)]

I'm marking this as also affecting me using Ubuntu 18.04 and Firefox 62.

I don't ever see this problem with either Chrome or Chromium 69. Will look for upstream reports and link to anything relevant that I find later as bugzilla.mozilla.org horrendously slow at present.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Rex (rex.prestige)]

This issue persists in the recently issued version 62.0.3.

[Rex (rex.prestige)]

This issue persists in 63.0~b12+build2-0ubuntu0.16.04.1~mt1 .

[Rex (rex.prestige)]

I now notice that the PPA information asks that I not submit the bug report here, but instead via apport. I will try to submit that way, and try to keep this launchpad listing updated if I hear more.
P.S. This issue persists in 63.0~b13+build1-0ubuntu0.16.04.1 .