Note that these particular tiddlers are only available if you install the "browser sniff" plugin.
To do that, go to the $:/ControlPanel, select the "plugins" tab, and press the big blue "Get more plugins" button.
This will display a modal dialog. Press the big green "Open plugin library" button, and you will find an entry for:
Browser sniffing
$:/plugins/tiddlywiki/browser-sniff
5.1.21
Press the "install" button to add it to your current TiddlyWiki document. Then save-and-reload for it to take effect.
Once that is completed, you will find $:/info/browser/name and $:/info/browser/version now exist in your document.
enjoy,
-e