• A quick additional detail: when I use my work VPN, Google sites load normally as well. So it seems the problem is with PIA... ?

When I try and load Gmail or any other Google site, I get a blank page and nothing loads at all. This only occurs when my VPN is on (I use Private Internet Access).

Sounds like a VPN issue to me. To test it, just open Firefox in Safe Mode see if you still have the same issue.

Try clearing site cookies and disabling Tracking Protection for the site.

Does it still happen in Troubleshoot Mode?

Minimal Gravitas said

When I try and load Gmail or any other Google site, I get a blank page and nothing loads at all. This only occurs when my VPN is on (I use Private Internet Access).

Sounds like a VPN issue to me. To test it, just open Firefox in Safe Mode see if you still have the same issue.

Thanks for getting back. I did open it in Safe Mode and had the same issue - this you would assume means it is a VPN issue, not Firefox? (But why does it work in other browsers? Surely these sites aren't only refusing to function for the combination PIA+Firefox and not PIA+Chrome or PIA+Opera...?)

Try clearing site cookies and disabling Tracking Protection for the site. Does it still happen in Troubleshoot Mode?

Hi, thanks for replying. Yes, the situation persisted after I backed up my account, removed my profile, opened in Troubleshoot mode, refreshed Firefox, re-installed Firefox... everything I could think of to get the most vanilla, out-of-the-box Firefox experience.

I would be ready to believe it is just a VPN issue except... why is Firefox the only browser that is failing here?

This could be a problem with the TLS 1.3 Early Data feature also known as Zero Round Trip Time Resumption (0rtt). You can try to set security.tls.enable_0rtt_data => false on the about:config page to disable this feature.

See also:

• /questions/1376015 Issue with most Google sites on Firefox v100 64bit

I ended up resolving it based partly on the solution found here. TLDR: I had to change the VPN DNS settings.

I noticed that the DNS setting on my home WiFi was not stable; if the issue was coming from inconsistent DNS servers then this would not help. I deleted the default DNS servers and added a public one (OpenDNS... don't really know if some are better than others). Then I changed the PIA settings (have to do this in the desktop app itself) to "Use Existing DNS" . Setting it to "Custom" and pasting in the same DNS as I had just set in my computer's WiFi preferences did work too, mostly, but for some reason I kept getting an endless string of Captcha if I tried using Google services.

I don't know enough about why this occurred only while using Firefox to comment on that, but FWIW it does seem like DNS settings and inconsistencies matter with this browser in a way that they didn't for others, in this case at least.

Thanks all for your input.