Rendering in FF53ESR shows compression artifacts

[uli42]

Reported via x2go-user ML:

> about:mozilla in Firefox 45.9.0esr
> https://abload.de/img/ff-45esr-html1js43.png

> about:mozilla in Firefox 52.1.2esr
> https://abload.de/img/ff-52esr-htmllns35.png

> Differing quality between adjacent elements in Firefox 52.1.2esr
> https://abload.de/img/differing-quality-icow4s09.png

> Artifacts in the chrome seem to disappear when I resize the window and
> it has to be redrawn. They reappear after I hover on them (ie, after
> the backgound changes).

These screenshots definitely help to understand the issue. 

I can reproduce this by running an xterm in a x2go session on Ubuntu 16.04 to localhost in the default setting. Running FF45ESR and FF53ESR with a clean profile with about:mozilla shows the issue.

I have done some tests with the current nx development version. If you only use nxagent (as Xnest replacement) the rendering works. But as soon as the nx compression libs come into play the problem shows. Using nopack make the issue go away for me.

Update: For convenience and to ensure we do not lose them I cloned those images right into the issue.