[Firefox] Save/Load project buttons error: window.showOpenFilePicker is not a function

[oiale]

Steps to reproduce:

1. Go to https://zalo.github.io/CascadeStudio/ using Firefox v121+
2. Click 'Save Project' or 'Open Project'
3. Nothing happens, and console shows the following error:

Uncaught (in promise) TypeError: window.showOpenFilePicker is not a function
    getNewFileHandle https://zalo.github.io/CascadeStudio/js/MainPage/CascadeMain.js:535
    loadProject https://zalo.github.io/CascadeStudio/js/MainPage/CascadeMain.js:589
    onmouseup https://zalo.github.io/CascadeStudio/:1

Interestingly, the button 'Import STEP/IGES/STL' works correctly and shows a dialog.
Turning ublock on/off shows no difference.
Tested on

MacOS 14.2.1
Firefox 121.0

Windows 10 22H2
Firefox 121.0.1

[hadess]

Ran into the same problem trying to load https://www.printables.com/model/425966-parametric-sliding-lid-box
Same symptoms. Worked in Google Chrome in a pinch.

[jonasfa]

PSA: while it's disabled by default, Brave supports this browser feature if you enable the "File System Access API" feature flag in brave://flags/#file-system-access-api.