Thank you for expressing your concern.

Since the issue does not occur in Firefox safe mode, this issue is most likely caused by an addon. Judging from your list of addons that you have installed on your system, I would guess that the Classic Theme Restorer is the cause of this issue.

You can try disabling this addon to see if the issue goes away.

You can also try disabling graphics hardware acceleration. Since this feature was added to Firefox, it has gradually improved, but there still are a few glitches.

You will need to restart Firefox for this to take effect so save all work first (e.g., mail you are composing, online documents you're editing, etc.).

Then perform these steps:

1. Click the menu button and select Options on Windows or Preferences on Mac or Linux.
2. Select the Advanced panel and then the General tab.
3. Uncheck Use hardware acceleration when available.
4. Restart Firefox and see if the problems persist.

Did this fix your problems? Please report back to us!

If the problem is resolved, you should check for updates for your graphics driver by following the steps mentioned in these Knowledge base articles:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

• Upgrade your graphics drivers to use hardware acceleration and WebGL

Disabling hardware acceleration does away with the flickering problem. But, like I said, in safe mode the problem doesn't occur either. And iirc, in safe mode hardware acceleration is still enabled, right?

Anyway, regardless, this probably means you need to know about my graphics setup to solve the problem permanently:

2 videocards, both a GeForce GTX760 4GB, running in SLI. Driver is Forceware 361.91 (latest stable release at the time of writing). Attached are 3 monitors, all of them FHD. The middle one is primary, connected to card 1. Then on the left is monitor 2, connected to card 1, and on the right is monitor 3 connected to card 2. All DVI.

Hopefully this helps.

A small footnote: why does Firefox render the *entire* window on the GPU? Why not just the tab content? GUI's aren't usually rendered on the GPU like that, unless it's a game.

When you use Firefox in safe mode, it disables your hardware acceleration. Since disabling your hardware acceleration fixed the issue, this is the cause of the flickering.

Okay. So information on my GPU setup, is it enough to get the problem fixed? If you need anything more, please let me know.

If you would like to report the issue to the Firefox developers, please file a bug report on Bugzilla.

You could try updating graphic drivers, as has already been suggested, or conversely try rolling them back.

• Upgrade your graphics drivers to use hardware acceleration and WebGL

It would be a lot of effort trying to file a useful bug.

Does this happen on all tabs, including for instance a blank tab or about:about. ?

I'm not a huge fan of downgrading drivers. The updates are there for a (usually) very good reason. Besides, MS Edge is showing no problems at all. It's smooth as silk.

And yes, it happens on all tabs. Like I said, the *entire* window flickers, not just tab content. This is why I was a bit mystified about why the browserchrome is also rendered on the GPU - that's unusual.

I do not often use Windows, but I thought it was now pretty easy to temporarily roll back graphics drivers, if so that seems like a good troubleshooting step.

I have Windows 10 on one machine but do not see the problem. You already know there is no issue with hardware acceleration disabled on your machine, comparing graphics drivers narrows down the issue further prior to you filing a bug. If you do file a bug please let us know the bug number as others may be interested in following any progress on that.

Seems like graphics drivers make no difference. I've downgraded them to 358.91, which is the same as another similar win10 box that does not have this flickering problem. And I'm still getting flicker with HW accel enabled on this system only.