App.element.io shows blank opening screen in Firefox

[barthanssens]

Steps to reproduce

1. When I open https://app.element.io in Firefox (even in a private window), I only see a blank screen

Outcome

What did you expect?

"Welcome to Element" opening screen should be visible.

What happened instead?

Firefox just shows a blank screen (it works just fine in Chrome on the same laptop).
"View page source" reveals that there is HTML being loaded.

Using the developer tools, I noticed a few errors

Error while fetching an original source: unsupported protocol for sourcemap request webpack://element-web/node_modules/tslib/tslib.es6.mjs
Source URL: webpack://element-web/node_modules/tslib/tslib.es6.mjs

and

Uncaught TypeError: Intl.Segmenter is not a constructor
    node_modules bundle.js:2
    l tslib.es6.mjs:369
    tsx MediaDeviceHandler.ts:89
    l tslib.es6.mjs:369
    ts MatrixActionCreators.ts:369
    l tslib.es6.mjs:369
    ts MatrixClientBackedController.ts:30
    l tslib.es6.mjs:369
    tsx SettingLevel.ts:20
    l tslib.es6.mjs:369
    ts ConfigSettingsHandler.ts:68
    l tslib.es6.mjs:369
    tsx IntegrationManagers.ts:184
    l tslib.es6.mjs:369
    tsx DevtoolsDialog.tsx:147
    l tslib.es6.mjs:369
    ts RecorderWorklet.ts:1
    l tslib.es6.mjs:369
    c tslib.es6.mjs:369
    O tslib.es6.mjs:369
    <anonymous> tslib.es6.mjs:369
    <anonymous> tslib.es6.mjs:369
[Alert.tsx:91:2](webpack://element-web/src/components/Alert/Alert.tsx)
    js Alert.tsx:91
    l tslib.es6.mjs:369
    tsx MediaDeviceHandler.ts:89
    l tslib.es6.mjs:369
    ts MatrixActionCreators.ts:369
    l tslib.es6.mjs:369
    ts MatrixClientBackedController.ts:30
    l tslib.es6.mjs:369
    tsx SettingLevel.ts:20
    l tslib.es6.mjs:369
    ts ConfigSettingsHandler.ts:68
    l tslib.es6.mjs:369
    tsx IntegrationManagers.ts:184
    l tslib.es6.mjs:369
    tsx DevtoolsDialog.tsx:147
    l tslib.es6.mjs:369
    ts RecorderWorklet.ts:1
    l tslib.es6.mjs:369
    c tslib.es6.mjs:369
    O tslib.es6.mjs:369
    <anonymous> tslib.es6.mjs:369
    <anonymous> tslib.es6.mjs:369

Operating system

Debian 12 / Bookworm

Browser information

Firefox 115.13.0esr (64-bit)

URL for webapp

https://app.element.io

Application version

No response

Homeserver

No response

Will you send logs?

Yes

[t3chguy]

Firefox 115 is not supported as per https://github.com/element-hq/element-web#supported-environments
See #27684 for the request to support ESR