BApp details: Browser Repeater
This extension renders responses returned in the Repeater tool in a real browser (specifically Firefox).
You can install BApps directly within Burp, via the BApp Store feature in the Burp Extender tool. You can also download them from here, for offline installation into Burp.
Please note that extensions are written by third party users of Burp, and PortSwigger Web Security makes no warranty about their quality or usefulness for any particular purpose.