This is a weird one.
This is a new issue on an existing Ubuntu 14.04, dual screen setup, using Unity, nothing out of the ordinary. When I go to puzzling.stackexchange.com on my left monitor screen in either chrome or firefox, that screen turns black.
This does not happen on any other website, but does happen on every page on that site (that I've tried). Though there is a slight flickering on arstechnica.com's middle-gray gradient background. Because of this and the new redesign, I'd hypothesized that it's happening only on websites with gradients like that, but fullscreening gradient wallpapers from google images didn't give me any strange effects at all.
Going to puzzlingSE in a browser on my right monitor screen doesn't have that effect. If I drag the browser from the right monitor onto the left one, the left monitor turns black once I've gotten it mostly over there. It starts showing stuff again when I drag it back.
My left monitor (the one with the problem) is using an HDMI cable and the other (identical) monitor is using a DVI cable. I also replaced the HDMI cable with another HDMI cable; no help. The problem persists across rebooting.
Puzzling SE recently got a new site design, documented here. What could be going on?
lshw -c video gives:
*-display description: VGA compatible controller product: Curacao XT [Radeon R7 370 / R9 270X/370 OEM] vendor: Advanced Micro Devices, Inc. [AMD/ATI] physical id: 0 bus info: pci@0000:01:00.0 version: 00 width: 64 bits clock: 33MHz capabilities: pm pciexpress msi vga_controller bus_master cap_list rom configuration: driver=radeon latency=0 resources: irq:63 memory:e0000000-efffffff memory:f7e00000-f7e3ffff ioport:e000(size=256) memory:f7e40000-f7e5ffff
Taking a screenshot shows the webpage accurately, not a black screen. Moreover, while the "save screenshot" window is open, the black screen turns nonblack, displaying the webpage, but with the left monitor screen-tearing and flickering.
Update: I got another video card and installed the relevant nvidia drivers.
*-display description: VGA compatible controller product: GF119 [GeForce GT 610] vendor: NVIDIA Corporation physical id: 0 bus info: pci@0000:01:00.0 version: a1 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress vga_controller bus_master cap_list rom configuration: driver=nvidia latency=0 resources: irq:62 memory:f6000000-f6ffffff memory:e8000000-efffffff memory:f0000000-f1ffffff ioport:e000(size=128) memory:f7000000-f707ffff
filename: /lib/modules/3.13.0-91-generic/updates/dkms/nvidia_367.ko alias: char-major-195-* version: 367.27 supported: external license: NVIDIA srcversion: 513914449E3DDF807584E74 alias: pci:v000010DEd00000E00sv*sd*bc04sc80i00* alias: pci:v000010DEd*sv*sd*bc03sc02i00* alias: pci:v000010DEd*sv*sd*bc03sc00i00* depends: vermagic: 3.13.0-91-generic SMP mod_unload modversions parm: NVreg_Mobile:int parm: NVreg_ResmanDebugLevel:int parm: NVreg_RmLogonRC:int parm: NVreg_ModifyDeviceFiles:int parm: NVreg_DeviceFileUID:int parm: NVreg_DeviceFileGID:int parm: NVreg_DeviceFileMode:int parm: NVreg_UpdateMemoryTypes:int parm: NVreg_InitializeSystemMemoryAllocations:int parm: NVreg_UsePageAttributeTable:int parm: NVreg_MapRegistersEarly:int parm: NVreg_RegisterForACPIEvents:int parm: NVreg_CheckPCIConfigSpace:int parm: NVreg_EnablePCIeGen3:int parm: NVreg_EnableMSI:int parm: NVreg_TCEBypassMode:int parm: NVreg_MemoryPoolSize:int parm: NVreg_RegistryDwords:charp parm: NVreg_RmMsg:charp parm: NVreg_AssignGpus:charp