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Comment by NikolaeVarius | Hacker News Reader

I find that Firefox/Firefox-Dev seems to be very VERY slow on my 4k setup. It works just fine when not connected to the 4K monitor, but when connected, sites take like 5x longer to properly fully load. I've tested it with the Debug stuff on, and it simply just shows render times being very very slow with nothing else. It also pegs the CPU 100% while loading.

There are no errors, but I notice a LOT of GC Pauses in the perf dump

Chromium works just fine on these sites.

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If you've got a specific site that this reproduces on that would be helpful. If you can also provide the model of the monitor you're using and the version of your OS that would help us track it down. Thanks!

Not a specific site, just general slowness on all rendering.

This is with fully clean install and several attempts at cleaning profile. I notice it seems to get stuck on "waiting for site" and "Performing TLS Handshake", which is strange because im on a 100gbit line and I can get chrome to load those sites full speed just fine simultaneously.

X1 Carbon Fedora 26 Intel Core i7-6600U 16 GB RAM

Mesa DRI Intel(R) HD Graphics 520 (Skylake GT2)

Do you have a good place to send these profile dumps to?

If you're using GNOME 3, pressing Alt+Ctrl+Shift+R screen recording will start. There should be a red icon on the message tray in the right-bottom corner of your screen. If the message tray is hidden, Super+M will activate it. Pressing the red icon will stop the recording.

Posting the videos of Chrome vs Firefox Quantum somewhere like YouTube might be an interesting thing to watch.

> ... im on a 100gbit line ...

How'd you get a 100 GbE NIC in that X1 Carbon!? :)

I imagine that’s the upstream :)

My situation is the opposite: workstation with a 10gbe connection the the corporate lan but upstream is capped to 2gbe.

Weird. I have a 4k display as well and my experience is not what you describe. I'm running macos high Sierra and there's no issues for me.

Restart firefox after you connect your screen--I've found on my linux laptop that connecting an external monitor with firefox open makes it freeze or be prohibitively slow. You may have a different problem--but just in case.

After doing that I've run it on my laptop's 4k screena nd a 4k external monitor on integrated graphics with no performance problems whatsoever.

Had the same experience with 4k. Would be interesting to hear from Mozilla on what is causing the issue.

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