Clipping forced on for desktop Firefox

[CendioOssman]

Describe the bug When using Firefox, clipping is forced on, and you have to use the drag panning move instead of using scroll bars when the session is larger than the browser.

To Reproduce Steps to reproduce the behavior:

1. Open settings

Expected behavior It should be possible to change "Clip to Window".

Client (please complete the following information):

• OS: Fedora 35
• Browser: Firefox
• Browser version: 102

Server (please complete the following information):

• noVNC version: 832937292ef09ede7da69923398ba79e69ca278d
• VNC server: TigerVNC
• WebSocket proxy: websockify

Additional context This is likely fallout from #1341.

It also seems that this is new behaviour for Firefox 100, where scroll bars now hide when not used. There is a new setting for Firefox to get the old behaviour back. If you enable this and reload, then clipping is no longer forced.

[CendioOssman]

It seems some details have changed, or were overlooked on #1341.

First of all, a default macOS machine will not need #1341. By default scroll bars are permanently shown if there is a mouse connected. However, this can be disabled and scroll bars are instead only shown when actively scrolling. So the fix in #1341 are needed depending on configuration.

Chromebooks behave like Firefox does now, i.e. the scroll bar hides after a while and then reappears once you move the cursor close to it. At least for normal pages. This behaviour is broken with noVNC for some reason. Which is probably why #1341 was mistakenly thought to be needed for them as well.

Google are also doing something magical for Chrome web store, where they are able to force scroll bars to always be shown.

[CendioOssman]

Reported lack of detection to Firefox:

https://bugzilla.mozilla.org/show_bug.cgi?id=1786016