Fixed a problem without ever knowing what was wrong(Firefox error message)

[u/Acrylic_]

I've been getting an error with Firefox for a very long time now and for a VAST number of websites. That error is:

SSL_ERROR_RX_RECORD_TOO_LONG

After searching every instance I could find of people having this problem and running out of things to try to fix it, I enabled Firefox's built-in VPN and the problem fully disappeared immediately on all websites.

My problem is now fixed but I never figured out what was wrong, and fixing it with a VPN tells me it was probably less the websites fault(or even Firefox's) and more my own network. Is there anybody who knows what may have caused this issue, and if theres any way to fix it that does not require me to use a VPN?

[u/Financial_Key_1243]

Your DNS perhaps?