Which web page are you on when this happens?

It was a bing.com page but other web sites can cause this message.

What causes this message to appear?

”Webpage is slowing down your browser” This is the new way the browser tells you there is a problem with the script program(s). https://support.mozilla.org/en-US/kb/warning-unresponsive-script?cache=no

So that would mean if no scripts where allowed in a web page that the message should never appear. right?

That depends on the real cause of the problem.

So htat goes back to my original question.

What causes the message "a web page is slowing down your browser" this message appears on all 3 operating systems I use.

https://support.mozilla.org/kb/Clear+Recent+History#w_how-do-i-remove-a-single-website-from-my-history

Remove History For One Site

Open the History Manager <Control><Shift> H. In the search bar, enter the name of the site. Right-click on one of the listings and select Forget About This Site. This should remove all information, including any passwords / settings.

That does not answer my question on how Firefox identifies a web site as slowing down.

Does FF have a measurement metric how is it used?

Yes. Firefox keeps watch on the programs(scripts) it is running. If a program runs too long, an error message is displayed.

What I am still looking for is at what point does FF say "a web page is slowing down your browser"

What would a script have to do or how slow does web site have to slow

There are settings in the about:config page, but I don't remember what one.

Is there a list of all about:config parameter?

http://kb.mozillazine.org/Firefox_:_FAQs_:_About:config_Entries

See also comments in the Firefox source code.

• https://dxr.mozilla.org/mozilla-release/source/modules/libpref/init/all.js
• https://dxr.mozilla.org/mozilla-release/source/browser/app/profile/firefox.js

Note that some preferences are hidden and have a fixed default value and only show on about:config when you give them a value.

Are firefox users allowed to change or make corrections to source code cor-el?

How can anyone use the source code you proivded?

This happens on the New York Times web site (other places too.) I would really like to be able to use it. Pages also load very slowly. On Task Manager it says Firefox (5) or Firefox (6).

kj2008 said

On Task Manager it says Firefox (5) or Firefox (6).

More than one process is normal for the current Firefox. http://www.ghacks.net/2016/07/22/multi-process-firefox/

Multi-process Firefox is codenamed "e10s". https://wiki.mozilla.org/Firefox/multiprocess

Good to know about the Firefox (5) or Firefox (6). Could it just be unable to do so many things at once on this computer?

I have experimented with reducing the upload speed and noticed the message appears more often.

However I was hoping to find a definitive value. does it count the number of TCP retries?

I am still getting this yellow bar error, often on the NY Times web site. This is not the only place it happens. It also seems to momentarily "forget" that I have logged in. I've looked at Task Manager but don't see what I could do when it says Firefox is using a lot of memory at the time. I don't have much if any extra stuff on Firefox. Using Windows 10 and probably have a slow connection.