Clicking a link results in a "Firefox is already running" window

### Steps to reproduce

1. Click a link sent to me in a chat (or even the one to open a Github issue in the settings) while Firefox is already running (on Linux)

### Outcome

#### What did you expect?
A new tab should open in the running Firefox

#### What happened instead?
A window pops up telling me that Firefox is already running and should be closed first

### Operating system

Linux

### Application version

Element 1.9.9

### How did you install the app?

Debian package

### Homeserver

Not relevant here

### Will you send logs?

No