The World Wide Web was built over the Hypertext Transfer Protocol (HTTP)
and the Hypertext Markup Language (HTML).
A User Agent, like a web browser, uses HTTP to request a HTML
document. The browser then formats and displays the document to its
user. HTTP is used to transport more than HTML, but HTML is the lingua
franca of the Web and web applications.
It was mangled badly in this commit. I'd suggest reporting a bug, and maybe submitting a patch to restore the original wording.
The adverb ever is mainly used in negative and interrogative sentences to mean "at any time". Besides, it is used for emphasizing that something has never happened before or should never happen.
In the first sentence, the last ever concert means that it's the last concert that the archestra is going to perform; it will not perform again in the future.
In the second sentence, "the first ever fall in profits" means that it's the first time that there has been a fall in profits; there has never been a fall in profits before.
The author really wants you to use either the Tails or the Whonix operating system to conduct whatever activities you wish to accomplish. And if you're using a different operating system, they are telling you it's OK to use Tor Browser on that operating system, but only to obtain Tails or Whonix.
They are saying you shouldn't use Tor Browser for any purpose on any other operating system except to obtain Tails or Whonix.
Best Answer
This seems to be a mistake. The original documentation, from 2013, reads:
It was mangled badly in this commit. I'd suggest reporting a bug, and maybe submitting a patch to restore the original wording.