What's going on is that, Twitter is switching me to their "mobile" site after it detected my browser was outdated. Factly I can still send Tweets, its just their mobile site. My experience with websites that doesn't support old browsers is that they disable all the features to help staying safe.
"You are on Twitter Mobile because you are using an old version of Firefox. Learn more here"
I've read the last part of the above in-answer comment. There was one line I memorized saying "..including all the latest features and security updates, please make sure your browser and operating system are up-to-date."
The reason for this wasn't clear for me at all.
Why is Twitter switching to their mobile site, while using all the twitter features is still a thing?
Does this mean their mobile site is more secure?