Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and

• Remove Cookies
  Warning ! ! This will log you out of sites you're logged in to.

Type about:preferences<Enter> in the address bar.

• Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
• Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} A small dialog should appear. Click Start In Safe Mode (not Refresh). While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe websites. Are there any problems?

Then restart.

I've done all of the above with no success.

Your useragent seems to have been reported correctly to this site. Do you use any privacy-oriented add-ons that could be modifying it on a site-by-site basis? How about external software or a proxy/Private VPN service?

No, no add ons that are recent, and I tried starting in safe mode with no luck. No external software or vpn service either. I am tethered via my android phone as internet service, but I've always done that with out having this issue before.

frustrated66 said

I am tethered via my android phone as internet service, but I've always done that with out having this issue before.

I agree. Tethering should not modify your actual requests if that Android feature is operating normally.

Does the problem affect both HTTPS and HTTP connections, or only HTTP? For comparison:

• https://www.jeffersonscher.com/res/jstest.php
• http://www.jeffersonscher.com/res/jstest.php

It appears to only effect http sites

Perhaps there is some software on the Android device that is proxying the connection. If you check bandwidth usage, does anything seem unusually high that could be a "man in the middle"?