`server connection lost` every 15 seconds only in Firefox

[uh-zuh]

Describe the bug

Page is reloaded every 15 seconds only in Firefox (Windows).
Chrome, Opera, Edge - no page reload.

Reproduction is started Svelte project.

There are no any Vite logs during connection lost.

Logs in Firefox console:

[vite] server connection lost. Polling for restart...
[vite] connected from window
[vite] connected from window
[vite] new window visibility visible
[vite] ping successful
[vite] connecting...
[vite] connected.

Reproduction

https://github.com/uh-zuh/vitejs_vite_bug_connection_lost_firefox

Steps to reproduce

1. Clone repository
2. run run-dev.sh/run-dev.cmd
3. Navigate http://localhost:5173/ from desktop Windows Firefox
4. Wait 15 seconds
5. See page reload

System Info

System:
    OS: Linux 6.6 Debian GNU/Linux 13 (trixie) 13 (trixie)
    CPU: (3) x64 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz
    Memory: 3.71 GB / 7.76 GB
    Container: Yes
    Shell: 5.2.37 - /bin/bash
  Binaries:
    Node: 26.7.0 - /usr/local/bin/node
    npm: 11.19.0 - /usr/local/bin/npm

Used Package Manager

npm

Logs

Failed to paste Vite initialzation logs because of error: Field can not be longer than 65536 characters

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[bluwy]

Can you also share the Firefox version you're using? Perhaps it's a bug in one of their new versions.