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Add-on not installed/downloaded due to connection failure

  • 8 replies
  • 7 have this problem
  • 6690 views
  • Last reply by John99

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This has been going on since I redownloaded firefox. I keep getting the error "Add-on not installed/downloaded due to connection failure", This is not limited to one app, this is limited to several apps. I know nothing is wrong with my connection because, well I am connected to the internet on my computer just fine.

I have searched to try to find a solution but nothing has helped, I even did "New>String and name it: xpinstall.enabled and set the value to true" and restarted firefox but that did nothing at all.

It seems to be a firefox issue and this one of many issues that I'm having.

Chosen solution

I thought that it might be at first my Antivirus software, But I'm not sure what about that software is preventing me from downloading add-ons.

Maybe your AV software is suspicious of the downloads.

Those addons are third party software hosted on third party sites. It is possible they no longer work with Firefox even if they will download. I am not going to risk trying a test download of them myself.

The Mega site does apparently have a download, that appears to be an addon of the Firefox extension type dot.xpi file. The Honey site I did not notice any download offered, but I did not try joining or logging in.

Have you considered officialy hosted addons:


I tend to be rather suspicious of free addons that are not hosted on the official Firefox site.

  • Why are they not hosted on the official site ?
  • Possibly because they are harmful to Firefox or your privacy.
  • You could ask that on the honey and Mega support sites
    • I notice the Mega site says And if you're really paranoid: ... scrutinize our source code for each update manually. , but I do not see it offering the actual addon as a file you may inspect and rename before installing.
    • If the .xpi addon from Mega installs on Firefox 48 at least that indicates it is a signed addon and hopefully not harmful.
    • I wonder why I see code mentioning bitcoins on that Mega page e.g.
      <a class="btn-open-wallet" href="">Open Bitcoin wallet app</a>
      Maybe I am being paranoid
  • No idea if Honey is offering a Firefox extension or for instance some Windows Executable able to affect the whole computer.

Security related software often bundles free additional toolbars etc as third party addons and they cause endless problems with Firefox, and often require updating on each update of Firefox every six weeks or so, but the third party update availability may not coincide with the Firefox update so for a while the addon, Firefox or both may be broken.

If you do decide to use such addons consider doing so from a new additional Firefox profile. That may limit the damage they could do. The profile manager allows you to choose which profile to use.

There are even methods of running two instances of Firefox and using two profiles simultaneously.

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I forgot to mention my computer specs, I'm on Windows 7 64Bit, Using the latest updated version of Firefox.

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Try creating a new additional profile for test purposes. Keyboard shortcut Winkey + R gets you a Run prompt and key in or paste firefox.exe -P and press Enter to get the Profile manager. Use the suggested location, and give it a short meaningful name 2016-001 would do.

Do not delete or rename any profile you create. Using the profile manager again lets you choose which profile to use, or set one to be used all the time.

You could try the Firefox Refresh but although it is supposed to be an idiot proof quick click option it is nowhere near as easy to reverse its changes.

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Alright, I tried what you said with the new profile to see if the problem still persisted and it still does.

I'm not sure why I keep getting the "connection failed" clearly my internet works fine, its Firefox saying otherwise.

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I did recently see someone else having a problem with downloading ad-ons, not sure if there is any reason for this and whether that has anything in common with your problem, other than both are so far unresolved.

If you still have a problem with a new Firefox profile it is not going to be any setting you changed in about:config that is causing a problem.

The mozilla site itself looks ok and I recently downloded an add-on with Fx48 on Windows. So no reason to think it is a general problem.

Are you able to download other files ok from other sites ? What about this forum site ? Right click on an avatar from this forum and try to save it. That will result in a small file download. Does that download ok ?

Some of those potential fixes are effectively done by using a new profile.

I guess you may need to look carefully at any security related software that you use. Also try some other addon download. What add-on downloads do not work for you ? I will check they work for me if you provide a couple of links.

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The forum download went good, Its just some of the add-ons that I try to download for firefox say that its failed due to a "failed connection" but I know that my internet is fine because I'm browsing just fine.

Just 2 Add-ons

Mega Firefox Extension: https://mega.nz/#firefox Honey: https://www.joinhoney.com/install

I thought that it might be at first my Antivirus software, But I'm not sure what about that software is preventing me from downloading add-ons.

I have 2 active antivirus software, One is Premium Malwarebytes Pro, and the other is Kaspersky Total Security Version 17.0.0.611(a)

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Chosen Solution

I thought that it might be at first my Antivirus software, But I'm not sure what about that software is preventing me from downloading add-ons.

Maybe your AV software is suspicious of the downloads.

Those addons are third party software hosted on third party sites. It is possible they no longer work with Firefox even if they will download. I am not going to risk trying a test download of them myself.

The Mega site does apparently have a download, that appears to be an addon of the Firefox extension type dot.xpi file. The Honey site I did not notice any download offered, but I did not try joining or logging in.

Have you considered officialy hosted addons:


I tend to be rather suspicious of free addons that are not hosted on the official Firefox site.

  • Why are they not hosted on the official site ?
  • Possibly because they are harmful to Firefox or your privacy.
  • You could ask that on the honey and Mega support sites
    • I notice the Mega site says And if you're really paranoid: ... scrutinize our source code for each update manually. , but I do not see it offering the actual addon as a file you may inspect and rename before installing.
    • If the .xpi addon from Mega installs on Firefox 48 at least that indicates it is a signed addon and hopefully not harmful.
    • I wonder why I see code mentioning bitcoins on that Mega page e.g.
      <a class="btn-open-wallet" href="">Open Bitcoin wallet app</a>
      Maybe I am being paranoid
  • No idea if Honey is offering a Firefox extension or for instance some Windows Executable able to affect the whole computer.

Security related software often bundles free additional toolbars etc as third party addons and they cause endless problems with Firefox, and often require updating on each update of Firefox every six weeks or so, but the third party update availability may not coincide with the Firefox update so for a while the addon, Firefox or both may be broken.

If you do decide to use such addons consider doing so from a new additional Firefox profile. That may limit the damage they could do. The profile manager allows you to choose which profile to use.

There are even methods of running two instances of Firefox and using two profiles simultaneously.

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I didn't know that honey had an official add on for Firefox, I just downloaded it since you mentioned it.

The iMega one though, I think that I will just pass on the mega extension all together.

Thank you for all your help.

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You are welcome.