Web pages with infinite scroll get incredibly laggy

Some more info, reloading the pages to start over do not alleviate symptoms, the browser has to be fully closed. I'm not sure if closing the page and opening it again later does it, in case it's a memory releasing problem.

It ALSO tends to impact performance of other tabs a little bit.

Task manager as in about:processes consumption breakdown? Task Manager - see whether tabs or extensions are slowing down Firefox — i.e. these all look like not leaking memory, no off the charts resource hogs by the tabs or addons etc.?

Generally once you close off all instances of the tabs for given domain, its process should be removed so ideally these wrinkles do not leave behind any mess. The complicated thing that can bridge the gap between the process resources is Service Workers support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox#w_application-basics so check their processes on the task manager as well.

See if trying out some presets to capture profiler.firefox.com/docs show anything immediately visible for you when the slowdowns start.

I did mean the Firefox process manager.

I did some profiling of one of the troublesome websites, but I don't know what to look for. I saw all the JANK bars in red at the top typically whenever the symptoms were occurring, but I have no idea how to parse anything else about this log. I'm not a programmer nor am I tech-savvy enough. I didn't see a guide for how to find sources of jank, is that right?

Could you reproduce the same in Troubleshoot Mode? (in Help menu)

If you instead of reloading the page close all tabs belonging to that service, and open a new one, is that one still affected?

If you remove these sites' workers from about:serviceworkers when they're stuck, is there any change?

Does anything change if you use that site in private window, and if it exhibits there, would closing out private mode and opening a fresh private window hit the same issue right away or would you get that clean slate performance again?

If you have any jank captured in a profile that's definitely something to look into. Could you upload the profile (the docs show how, until you upload it's local only, sharing it stores it on the profiler server for further investigations) and share the shortlink it gives you after it finishes uploading? Thanks! (FWIW: I suck at reading the profiles anyway, but it's a good start for filing a bug to have some data capture for the next person looking into it.)

Sorry, I forgot to mention troubleshooting mode.

The problem still exists on both websites in troubleshooting mode. For what it's worth it also exists in a completely fresh install of WaterFox, though I know that doesn't say much.

I'm not entirely sure if closing the page and opening a new one instead of refeshing does it. It definitely seems like other pages from the same site are affected e.g. if twitter is scrolled down like a hundred Page Down presses or something, other twitter tabs suffer when trying to scroll down.

I'm going to try the service worker thing for twitter, but bluesky does not have one or I can't figure out what it's called, so I don't think that one's what's going on.

So I unregistered twitters service worker and unloaded the tab, then started browsing again from the top, and it seems like unloading probably reset it or something. Hard to say so far whether the service worker thing did anything especially since I can't do it with Bluesky. I'll have to figure out something

Yep, safemode to eliminate addons, separate profile/binary for comparison, that's all good steps.

Why closing out tabs: pages' content processes are spun per origin… so if.a process starts struggling, it takes down all tabs of the same site. That's why instead of refreshing (that keeps the same process) closing out site's tabs to spin down its process and get a new one later. The worker is a cherry on top, as that one can keep the origin process spinning;) So if there's none, the better. But that's all just to "recover" from the jank — not getting to the bottom of it.

If you can try turning off your ESET endpoint security for a bit to test, to see if it's not stalling those long running processes with lots of connections…?

Here's a "firefox" preset profile of bluesky.

Here's a "web developer" preset of it.

Here's a "network" preset.

Here's a "web compat" one.

Lastly, here's a "debug" preset.

I can't believe I keep remembering missing information, but a laptop I installed Firefox on last week also exhibited the same symptoms on the same websites even when nothing else was running. I had synced my profile and extensions and such to it, though since it happened in troubleshooting mode anyway, I don't think that matters much.

Also, how do you know what security software I'm running? Related to that, I tried to toggle it off but it said something was recently found and I shouldn't disable it, so I opted to keep ESET active for these.

Various security suites do their job by hooking into running apps (causing crashes, network hangs, decryption/MITM errors or compromise the trust stores) — so their DLLs if known are noted in any support/troubleshooting profiles, to quickly pinpoint the worst offenders;]