Favicon & Favicon Message Badge Don't Work With Privacy/Fingerprinting Firefox Features

### Steps to reproduce

This appears to be similar to/related to: https://github.com/element-hq/element-web/issues/10146

This one confirms the badges on a favicon though, and it's not the case with Discord or other chat applications, so Element does something different to those alternatives:

---

A user has just reported that when `privacy.resistFingerprinting` is `true` in Firefox (about:config), Element's Favicon doesn't display unread notifications, substituting a grey box. You have to also set `privacy.resistFingerprinting.autoDeclineNoUserInputCanvasPrompts` to `false` to get Firefox to prompt you to allow HTML5 Canvas for Element to work properly. Discord and other chat tabs don't seem to have this issue, so I'm not sure what Element is doing differently to fall afoul of the `privacy.resistFingerprinting` setting.

I confirmed this on my own machine, and found the above "fix" of `privacy.resistFingerprinting.autoDeclineNoUserInputCanvasPrompts` = `false`

### Outcome

#### What did you expect?

Favicon remains as the Element icon, and chat/message notifications work on the favicon.

#### What happened instead?

Favicon is a grey/lined box, badges don't work.

### Operating system

any

### Browser information

Firefox

### URL for webapp

app.element.io

### Application version

current

### Homeserver

n/a

### Will you send logs?

No