Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. A small dialog should appear. Click Start In Safe Mode (not Refresh).

Is the problem still there?

Start your Computer in safe mode with networking. Then start Firefox. Try Safe websites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Hopefully you haven't recently installed some web-distributed malware pretending to be an urgent Firefox update. It would have been a redirect to a tab with the Firefox logo and an orange background. Numerous users have reported these sites in recent weeks.

Just in case, please scan with Malwarebytes Anti-Malware:

https://www.malwarebytes.com/mwb-download/ (free version)

AndyH-FF said

If I Restart with Add-ons Disabled, the network activity ceases but if I instead individually Disable every add-on and plugin shown in the Add-on Manager, network activity stays high (even after closing and restarting the browser).

I see in the Firefox Health Report, under Active Add-ons, the number 6 for extensions, but only three extensions are listed by the Add-on Manager. All of this strongly suggest to me that something is going on, out of sight, in the browser. How can I find it and get rid of it?

Next to your question, under Question Details > More System Details, you have six extensions listed. Some of these are downloaded by Firefox, some are added on. The Firefox ones do not appear under Extensions on the Add-ons page:

• Adblock Plus 2.7.3
• Firefox Hello 1.3.2 -- installed by Firefox
• Mozilla Archive Format 4.0.1
• Multi-process staged rollout 1.0 -- installed by Firefox
• Pocket 1.0.2 -- installed by Firefox
• Show Selected Images 0.18

The three "extension" listed are information but I can't say if they are helpful because I don't know if they are part of the problem.

My updates to Firefox, which I do frequently, are via Help/About Firefox/Check For Updates, then Install Update if there is any. I never see any other web page. Can this redirect work this way?

Updates to the add-ons are done via Tools/Add-ons/Check for updates. Again, if there are any they are installed without me ever seeing any other web page.

I will look into this Malwarebytes Anti-Malware (free version) but probably can't use it. Once upon a time, when downloads could generally be downloaded, transported to my computer via a flash drive and installed without more downloading, much was possible. Generally these days, the download and install are a single operation. My connection would probably take two days to do this -- if I could leave the phone line tied up that long and if I could actually download something that large without many failures requiring Restart the process so it can fail again.

ADDITIONAL INFORMATION I've been viewing this problem for for a week or so. Today, as soon as I made my first post in this thread, it stopped. I was able to visit several web sites with what used to be normal speed. Network traffic stopped once a page was loaded. Probably coincidence. Probably it happened sometimes earlier without my noticing.

However, as soon as I signed here in to read the replies and start this response, excess traffic resumed.

I don't know what Firefox Hello 1.3.2 -- installed by Firefox, Multi-process staged rollout 1.0 -- installed by Firefox, and Pocket 1.0.2 -- installed by Firefox are, and probably don't want them, but I guess I can go through the slow and tedious process of looking them up (any web page loading in five minutes is really fast here).

Can any of them be acting on their own? Could any of them be responsible for downloads when I don't want to be downloading ANYTHING I didn't specifically request? Might they be automatically updated even when I have turned off every automatic update I can find? Can I get rid of (or totally disable) them?

AndyH-FF said

However, as soon as I signed here in to read the replies and start this response, excess traffic resumed.

This site has an activity monitor that fires on each keystroke while you are typing a reply. I don't know if there is a way to disable that.

I don't know what

• Firefox Hello 1.3.2 -- installed by Firefox,
• Multi-process staged rollout 1.0 -- installed by Firefox, and
• Pocket 1.0.2 -- installed by Firefox

are, and probably don't want them, but I guess I can go through the slow and tedious process of looking them up (any web page loading in five minutes is really fast here).

I doubt it's worth the effort because all users have those and unless you are using the Pocket feature, they shouldn't be using the network.

It probably isn't terribly relevant but I almost never key into the browser. My posts here were done in a word process, then entered with copy and paste. All that time task manager showed virtually full bandwidth (such as it is) downloading. Nothing was going into the browser, or being visibly done by the browser to account for it.

There was a problem with a four year old version of the Malwarebytes program that would not run, would not uninstall, but prevented update/replacement by the new version. I didn't have time to fiddle with it for some days.

This evening I fixed that problem, installed the latest version, and scanned. It found nothing. The problem is still the same:

• dial in to get online
• task manager shows no network activity of significance
• open Firefox (I use no start page. The browser is loaded but not going anywhere)
• something starts downloading about as fast as the connection will handle. It does let me load and use web pages but response and loading are definitely much slower, due, I assume, to bandwidth being used by this what-ever-it-is. This is kind of like the BITS service. However, Windows Update is always disabled unless I want it. Stopping and disabling BITS makes no difference to this noxious activity.
• close the browser and the downloading stops within no more than 5 seconds
• repeat as often as wanted, it is always the same

except

• sometimes when the browser is open and I am on a fully loaded page, the downloading will stop for awhile but by and by resume again.

Is there really no way to find out what is doing this?

Could you set Firefox to "Work Offline" and see what that does? First finish any ongoing form submissions and save any unsaved work, then:

• tap the Alt key to activate the classic menu bar
• File > Work Offline

Does that stop the Firefox activity?

Meanwhile, this article has information about the normal background traffic of the browser: How to stop Firefox from making automatic connections.

Work Offline does stop the downloading while Offline is activat but of course doesn't help when I want to do something online.

I went through the list on the How to stop Firefox from making automatic connections web page. One thing on that list doesn't match what is in my browser and also doesn't compute for me, that is I don't understand its last step.

Firefox also checks to see if any updates are available for your add-ons (extensions, themes) 1. 2. 3. At the top of the tab, click the "Tools for all add-ons" Add-on Tools Icon menu, uncheck Update Add-ons Automatically and then select Reset All Add-ons to Update Automatically.

In my copy of the browser it says Reset All Add-ons to Update Manually.

I had already long ago unchecked Update Add-ons Automatically. If I click on Reset All Add-ons to Update Manually, the change it makes for the Extensions or Plugins which provide Options for Automatic updates changes my previous choice of Off -- which seems to me to say "don't do automatic updates" to Default, which is separate from On and Off and is unexplained. The original installed setting was On, so On is logically the Default, the opposite of the Off that I want. I changed each back to Off. Regardless of what this setting might seem to me to be, what could Default for automatic updates possibly be except On or Off?

The various choices under Tools/Options I had active on the Privacy, Security, and Advanced tabs seem unlikely to have led to this recent change of behavior since they have been on for a long time. I am going to try some of them turned off, inactive, or whatever it says that means don't do anything for me, but don't have much hope that will be useful.

Some things under about:config, about which I knew nothing, seem useful, such as eliminating prefetching of various things, but those should only be active under initiating circumstances. I also changed most of the other settings listed there as indicated on the directions but my impression of those things don't seem to possibly explain this recent behavior of heavy downloading whenever the browser is simply open, even looking at no webpage, which ceases whenever I close the browser. Why would there suddenly be a change of browser behavior when those settings are what they have been for years?

Correct, having made the changes, there is still heavy downloading if the browser is open.

An aside. As recommended, I installed Malwarebytes, scanned, and found nothing. Today, as soon as I connected to the internet, heavy downloading began, before opening the browser. I rechecked the Malwarebytes updates option to verify that there is no option to turn automatic updates off. At first I had hoped that meant there were no automatic updates in the free version but I guess it means there is simply no way to turn automatic updates off. I uninstalled the program, which seems to have eliminated that problem.

I don't like the thought of the bother or the time required or the necessity of reestablishing all my options but I'm wondering if uninstalling Firefox with Revo Uninstaller under its most through scrubbing choices might help. Once Firefox is reinstalled maybe the problem will be gone.

However, I know from experience that some uninstalls, even followed by registry scrubbing with multiple programs, such as CCleaner, Gary Utilities, and one or two others I used to have prior to Windows7, can leave hundreds of registry entries. I have sometimes spent hours manually locating and deleting additional registry entries after the best efforts of several cleaner programs. Even then, the best manual effort can be unsuccessful because too many registry entries can contain no identifying characteristics (at least none I can recognize).

I think I am beginning to ramble uncontrollably.

You can closely simulate the factory settings by testing in a new profile.

Create a new Firefox profile

A new profile will have your system-installed plugins (e.g., Flash) and extensions (e.g., security suite toolbars), but no themes, other extensions, or other customizations. It also should have completely fresh settings databases and a fresh cache folder.

With Firefox completely closed, start up in the Profile Manager by pasting the following in the Start > search box (or the Run dialog) and pressing Enter to execute it:

firefox.exe -P

Don't delete anything here!

Any time you want to switch profiles, exit Firefox and return to this dialog.

Click the Create Profile button, assign a name like August2016, and skip the option to relocate the profile folder. After creating the profile, select it and start Firefox in that profile.

Any difference in activity?

When returning to the Profile Manager, you might be tempted to use the Delete Profile button. But... it's a bit too easy to accidentally delete your "real" profile, so I recommend resisting the temptation. If you do want to clean up later, I suggest making a backup of all your profiles first in case something were to go wrong.