Reported by @crimson raft
Open an existing conversation on ChatGPT (web) and scroll to an earlier message (not the latest).
Click “Create a thread from this message” (a.k.a. “Branch in new chat”).
Observe that a new browser tab opens to a URL similar to: https://chatgpt.com/c/WEB:<uuid>.
(Optional) In the new tab, try Ctrl+Shift+R (hard reload).
A new branched conversation is created starting from the selected message, and the new chat opens with the full conversation context up to that message.
The branch should appear in the chat list (e.g., as a “Branch” chat) and be accessible/reopenable.
A new tab opens to https://chatgpt.com/c/WEB:<uuid> but loads an empty ChatGPT interface (no conversation). After hard reload (Ctrl+Shift+R), it shows the “start a new conversation” screen, as if no branch exists.
Windows 11 Home (24H2); ChatGPT Web App; Firefox 148.0 (64-bit)