Clicking Screen reader causes the demo page to freeze

[LonKeyDotae]

Describe the bug
on firefox clicking on "Screen reader" under the "Backend" side panel causes the page to freeze and the following error to appear in the console:

Uncaught TypeError: can't access property "cancel", arg0 is undefined
__wbg_cancel_cad909b29551da17 https://www.egui.rs/egui_demo_app.js:469

imports.wbg.__wbg_cancel_cad909b29551da17 = function(arg0) {
    arg0.cancel();
};

Log attached below

2025-09-16.16-31-05.mp4

To Reproduce
Steps to reproduce the behavior:

1. Go to www.egui.rs
2. click on "Backend"
3. click on "Screen reader"

Desktop:

• OS: bazzite-gnome-nvidia
• Browser: Mozilla flatpak
• Version 142.0.1 (64-bit)

Additional context

firefox-console-export-2025-9-16_16-20-25.log

I couldn't replicate this on chromium, appears to be firefox only