Why does Firefox lag using NVDA on a page setting textContent? - javascript

Recently I've been testing my website using screen readers and ran into a page that lags like crazy when using NVDA. More specifically:
All browser actions are substantially delayed, but NVDA itself runs perfectly fine
For example, the page normally loads in its entirety in less than a second, but with NVDA active, the first image can take several minutes to render
Refreshing the page takes several minutes to execute
Even switching or closing the tab takes several seconds
After some extensive debugging, I isolated the issue into a rather specific set of criteria causing the slowdown:
This only happens on Firefox (I'm currently on Firefox 90); Chrome and Edge are fine
This only happens with NVDA; VoiceOver on Mac is fine even on Firefox. I do not have JAWS.
The action causing a slow down is setting an element's textContent on every requestAnimationFrame, so it's happening dozens of times per second
I am uncertain if this is experimentally significant, but I'm running on Windows 10 Home
I managed to scrape together a minimal CodePen example. I used CodePen here because the simplest way I could replicate the issue was by refreshing the page. In the example is a refresh button that activates a spinner, so if the page is fast the spinner will show up for only a brief moment; if it's slow then you'll get to observe the spinner in all its glory.
What I see when I try to refresh:
So while I isolated what is causing the issue, I have no idea why this is happening and hence how to solve my original page's problem without deactivating the widget outright.
What might be the underlying cause(s) of Firefox/NVDA slowing down on a page setting textContent?
Is there an alternative to setting textContent that I can or perhaps should consider?
Is this perhaps an issue that should be filed directly with either Firefox, NVDA, or both?
Thank you!
Addendum:
NVDA Github Issue: This open issue indicates long pages are slow to load, which may be related to my problem
My Website's Page: The page on my website I'm talking about

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I stashed all pending application changes to revert my application to a time when this was not a problem. The issue persisted.
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Final answer:
Remove all breakpoints
Even if they're not getting hit this fixed it for me and got performance back to normal.
May be a bigger issue if you have logging breakpoints - so try deleting those first if you're attached to your breakpoints.
Previous answers:
I came up with a workaround - although still not really figured out what is actually wrong.
I also discovered a bunch of tools I didn't even know existed that I'd skipped over before - they're under More tools.
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This is the behavior I got when choosing a date from mat-calendar. No other logic running - just selecting a date. I removed everything from app-component and just put a mat-calendar and it took ten seconds to change the date!
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Here's a few other things to try:
Test with --aot flag
This didn't make a difference to me, but good to narrow things down.
Add some controls that don't do anything (as a control)
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Just toggle them on and off, hide something.
<mat-radio-group>
<mat-radio-button [value]="false">
bloop
</mat-radio-button>
<mat-radio-button [value]="false">
bloop bloop
</mat-radio-button>
</mat-radio-group>
Enable Rendering debugging options
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<!-- yes, just a standard text box -->
<input type="text"/>
Just hide things with *ngIf="false"
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Especially if you have inspect tab open, that it's like a new page opened in the same time + has animations on any block render.
We had this issue today at a colleagues workstation. Turned out that it was a chrome-extension (don't remember, something with "ghost" in its name). So maybe try out using guest-mode and check whether the issue still occurs. If it doesn't, successively reactivate the extensions to see which one is causing the problems. If it still occurs, follow the other proposed approaches.

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