Firefox 153 Web CLI fails on FortiGate 7.2.13 while Chrome works (WebSocket NS_ERROR_GENERATE_FAILURE)

[Nascimento]

Hello,

I am facing a strange issue with Firefox 153.0 (64-bit).

Environment:

- Firefox 153.0 (64-bit)

- FortiGate 60F

- FortiOS 7.2.13 build 1762

- HTTPS management on port 8443

Behavior:

- Login to the FortiGate GUI works normally.

- All GUI functions work correctly.

- The integrated Web CLI widget immediately shows:

"Connection lost. Press Enter to start a new session."

When inspecting network traffic, Firefox shows:

main.js:1 (websocket)

NS_ERROR_GENERATE_FAILURE

What has already been tested:

- Cleared cache

- Cleared cookies

- Cleared site data

- Private browsing mode

- Firefox updated to latest version

- Certificate is accepted and TLS 1.3 is working

- No active enterprise policies

- No browser extensions

Important:

The exact same FortiGate and user account work perfectly in Google Chrome.

Has anybody seen WebSocket issues like this in Firefox 153?

Thanks.

[Nascimento]

Additional information: Firefox Network Inspector reports

Type: WebSocket

Initiator: main.js:1 (websocket)

Error: NS_ERROR_GENERATE_FAILURE

The FortiGate Web CLI uses a WSS (Secure WebSocket) connection.

The issue occurs immediately when opening the embedded CLI widget.