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

You might need to restart Firefox in order 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:

• Click the orange Firefox button at the top left, then select the "Options" button, or, if there is no Firefox button at the top, go to Tools > Options.
• In the Firefox options window click the Advanced tab, then select "General".
• In the settings list, you should find the Use hardware acceleration when available checkbox. Uncheck this checkbox.
• Now, restart Firefox and see if the problems persist.

Additionally, please check for updates for your graphics driver by following the steps mentioned in the following 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

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

Thank you.

Hi, and thanks for the answer!

I've disabled "hardware acceleration" but it didn't fix the issue... And my graphic driver is the very last one!

Does this only happen with "Energy Saver" Windows's power plan active or otherwise as well?

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Hi Cor-el!

No, it happens with "Balanced" power plan too. I don't know why, and that's so annoying.

Any solution?...

Did you check which settings are used in the balanced power plan and try to modify them selectively to a setting that works better to see if you can find a culprit?

Unfortunately yes... I've tried to turn on/off each settings of the balanced power plan and nothing change...

I had the same problem. This fixed it for me.

Click the orange Firefox button at the top left, select the "Options" button. In the Firefox options window click the Advanced tab, then select "General". Uncheck the box that says "Use Smooth Scrolling"

I have found a similar problem. I also use an XPS 15 9530, and had severe lag in some websites, such as feedly.com.

Some users have suggested disabling smooth scrolling, but that only makes the problem less aparent, but it is still there.

It turns out that for the HiDPI support I had layout.css.devPixelsPerPx set to 1.75.

I have found out that leaving it with the default value (-1.0), or setting it to 2, the scrolling is really smooth, as it should. I also get the slowdowns now if I set the zoom with CTRL+mouse wheel.

So, my experience is that setting the zoom one way or another to a non-integer value is what causes the slowdown. I have opened a bug for that: https://bugzilla.mozilla.org/show_bug.cgi?id=1007449

Can you try setting an integer zoom multiplier, and if that solves the issue for you as it did for me, comment on the aforementioned bug?