I can replicate this consistently on my computer, so I'm here to ask for help tracking down what's causing it so I can file a proper report.

Forgot to mention, this happens when I open comcast.com

Could you please open about:support, click on the "Copy text to clipboard" button, paste it into a text file and upload it here (Attach File)? Thanks!

Thanks! > Compositing: WebRender > NVIDIA GeForce GT 640

Doing a comparison of the before/after memory reports using the about:memory "load and diff" tool seems to indicate much of the memory is coming from JS/DOM, so I doubt this is specific to WebRender or graphics. It's likely a runaway script or some such. 3,580.98 MB (100.0%) -- explicit ├──1,313.42 MB (36.68%) -- js-non-window ├────885.13 MB (24.72%) ── heap-unclassified ├────835.95 MB (23.34%) ++ dom ├────503.27 MB (14.05%) ++ heap-overhead └─────43.21 MB (01.21%) ++ (21 tiny) ... 1,313.88 MB (100.0%) -- js-main-runtime ├────851.77 MB (64.83%) ++ realms ├────411.71 MB (31.34%) ++ zones ├─────31.04 MB (02.36%) ── runtime └─────19.36 MB (01.47%) -- gc-heap ├──18.36 MB (01.40%) ── chunk-admin └───1.00 MB (00.08%) ── unused-chunks 922.73 MB (100.0%) -- js-main-runtime-gc-heap-committed ├──856.08 MB (92.78%) ++ used └───66.65 MB (07.22%) ++ unused

(In reply to Jerod Lycett from comment #3) > Forgot to mention, this happens when I open comcast.com Is this just on the comcast.com home page? (For me that redirects to xfinity.com). Are you interacting with the page at all, or just leaving it idle? I let it sit for a few minutes and didn't see any increase in memory usage.

I've not poked around to see what pages it does happen on, but the my account page and the home page both do it for me. I don't interact with it at all, and can even leave it in a background tab and still have it occur.

Installed the latest nvidia driver, 398.82 released 2018-08-01 and problem still occurs. Also the runaway memory leak seems to keep running even after the tab is closed.

Does it happen if you have Webrender turned off as well?

Which settings should be changed? Both gfx.webrender.enable and force-disabled are false according to about:config.

Set gfx.webrender.force-disabled to true, restart the browser, and see if the issue still happens. Once you're done testing, please reset gfx.webrender.force-disabled back to default (false) and restart the browser again (it looks like you might have WebRender enabled via the shield study so it would be helpful if you continued testing that in general).

Yes, it does still happen with force-disabled set to true.

Thanks. So this isn't specific to WebRender - most likely a runaway script but considering it continues happening after the tab is closed, it might be a ghost window problem. Moving components.

Ooh, the about:memory report shows a ghost window denoted as "[system]". Andrew, do you know what that means?

I think I've seen that before, but I'm not sure what it means. By definition, I thought that ghost windows can only be content.

This sounds like an existing issue with WebExtensions causing high memory usage. I see a lot of structured-clone-holders in there.