It's still there in the 51.0.a1 nightly build.

There's a conversation on reddit about it (started by me) and also a bug report:

https://www.reddit.com/r/firefox/comments/4nfmvp/ff_47_unbearable_slow_over_remote_x11/

https://bugzilla.mozilla.org/show_bug.cgi?id=1263222

Stefan Seidel

-------------------------------------

On Sunday 28 August 2016 23:25:50 Stefan Seidel wrote:

> The variables gone by 50.Â~

>

> -_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_

> -_- Eskimo North Linux Friendly Internet Access, Shell Accounts, and

> Hosting. Knowledgeable human assistance, not telephone trees or script

> readers. See our web site: http://www.eskimo.com/ (206) 812-0051 or (800)

> 246-6874.

> On Mon, 29 Aug 2016, Stefan Seidel wrote:

> > Date: Mon, 29 Aug 2016 08:11:53 +0200

> > From: Stefan Seidel <sseidel@vub.de>

> > To: Jordan Sokolic <jordan@twiggle.com>

> > Cc: x2go-user@lists.x2go.org

> > Subject: Re: [X2Go-User] Web browser performance over X2Go

> >

> > Hi Jordan,

> >

> > Firefox 47 disabled XRender support by default. Go to about:settings and

> > search for xrender, set the property to true. That made it a lot better

> > for

> > me.

> >

> > Stefan

> >

> >> Date: Sat, 27 Aug 2016 12:34:32 +0300

> >> From: Jordan Sokolic <jordan@twiggle.com>

> >> To: x2go-user@lists.x2go.org

> >> Subject: [X2Go-User] Web browser performance over X2Go

> >>

> >> Message-ID:

> >> <CAFbFDtijPrfER_DEu+zM11N08FKb_Zn-WdUEkR99AQN1zZ9o=Q@mail.gmail.com>

> >>

> >> Content-Type: text/plain; charset="utf-8"

> >>

> >> Hello,

> >> I use a web frontend for work that runs locally on my server over X2Go

> >> for

> >> about one year with success.

> >> Some months ago I noticed a significant decrease in performance when

> >> using

> >> Firefox. My server is running Ubuntu 16.04 with MATE desktop, Windows 10

> >> client. Up to Firefox version 39.0.3 performance of loading pages,

> >> scrolling, browsing etc. was nearly flawless over a 5Mbit WAN link (with

> >> the exception of embedded video elements). However it seems the release

> >> of

> >> Firefox version 40.0 introduced some changes in rendering (see

> >> https://www.mozilla.org/en-US/firefox/40.0/releasenotes/) that do not

> >> play

> >> nice with X2Go. Further reduction in performance was noticed in versions

> >> 46.0 and 48.0. The current release (48.0) even has trouble rendering a

> >> plain text document without lag and choppiness.

> >> I have tried toggling various flags relating to graphics, compositing,

> >> rendering, etc. to no avail.

> >> To work around this problem the only solution I have found is to forward

> >> ports over a separate SSH tunnel and browse locally, but this is

> >> cumbersome

> >> to set up every time I need to connect.

> >> I have preferred Firefox to Chrome over X2Go because the latter has

> >> always

> >> been unusably slow; now they are both similarly choppy and slow.

> >> Has anyone else noticed this?

> >> Any advice or help would be appreciated.

> >>

> >> Regards

> >>

> >> Jordan