Twitter starts to showing warning to its users that the legacy version will be shut down on June 1st, 2020.
If you have installed a browser extension to trick Twitter into thinking you were running Internet Explorer 11, which is unsupported, Twitter would continue to show you the older site template.
For those who are using this trick to impersonate Internet Explorer 11, Twitter has started to display a warning that states this trick is going to stop working on June 1st, 2020, when they will shut down the original legacy version of Twitter.
“This is the legacy version of twitter.com. We will be shutting it down on June 1, 2020. Please switch to a supported browser, or disable the extension which masks your browser. You can see a list of supported browsers in our Help Center.”
The help article states that Twitter’s supported browsers are Firefox, Edge, Safari, and Google Chrome.