As of early November 2019, support for IE 11 has been dropped from SE's official compatibility matrix.
Edge is still supported, though I guess in 6-8 weeks I might ask about Edge (EdgeHTML) support in the era of everything being blink-based... if I'm feeling cheeky.
To state it:
IE 11 is still supported by the Manufacturer until 2025.
The EOL is in 2025. The same date that Windows 10 support will be dropped from Microsoft.
I don’t contest the support drop from SE, but any argument that it’s because it’s no longer supported by the manufacturer are not the real fact.
Rob's comment (above) triggered "more thinking", and I quickly found the culprit: I use an 'add-on' in Firefox called AdBlockPlus. I've used it for years, and never had a problem with Stack Exchange sites. However, when I added stackexchange.com to its whitelist, the 'banner warning' disappeared.
So - question in an answer:
What changed? What switch ...
I don't use the tab title, so I'm not bothered by your examples. What does bother me though is that tags often chew up valuable space in Google results instead of showing more of the title:
"proper nouns - Why are the United States often referred to as ..."
"legislative process - How would the United States of America grant ..."
"marvel cinematic universe - ...
Firefox for Mobile is not officially supported and never has been on our network. It has always been in a state of "it works but may break" in our list of supported browsers on Meta (which in fact still mentions version 10.0.3 from back in 2012).