We can be fairly sure that accounts.firefox.com is not incorrectly configured & I am sure it works for millions of others.

Try to check Firefox's internet settings are correct, and that security related software is not interfering

• How to troubleshoot security error codes on secure websites
• Advanced panel - Accessibility, browsing, network, updates, and other advanced settings in Firefox_network-tab
• Fix problems connecting to websites after updating Firefox
• Firefox can't load websites but other browsers can
• How to let Firefox use the internet on your Windows computer

Can you see none secure sites. Try with ones you have not previously tried. Try this one example.com or example.net

Also, apologies in advance, however if you have uninstalled Firefox please make sure to find the previous profile in the profile folder to sync.

I know accounts.firefox is working as I'm able to log into it via a different browser. none secure sites work fine, the problem just seems to be with secure ones. Every secure site seems to give me a connection is not secure error, I have to either import a certificate or it just wont let me access it. I have checked all the network settings and they are correct, I have also checked that my firewall isn't blocking firefox which it isn't. Currently if I try and sign into accounts.firefox I get this message "You must be connected to the Internet to sign in." with a big blue try again box. And yet I know I am connected as I was just checking non secure sites. The only thing that changed before reinstalling firefox was an update to the latest build of windows10 so it maybe a bug caused by that?

Check your version of Firefox please. Use Menu {three bar icon) -> Help { (?)icon) -> AboutFirefox It should be at least Fx44. Fx only updates over secure links and you could be still on Fx43. Fx44 relaxes security and so allows less secure certificates and so may not suffer this issue.

If necessary use an alternative browser to download the a new version of Firefox, but take care do not use any third party uninstaller just install Fx44 (soon to be Fx45) over the existing Firefox.

Forum Note Workaround for advanced users: Use about:config change pref security.pki.sha1_enforcement_level to have value 0 -  {accept all SHA-1 certificates)

My current version of firefox is 44.0.2. I have also tried using the latest beta and developers edition. Each time I deleted all the old profile information so that its a clean install just in case it was something in my profile causing the problem.

I have checked the security.pki setting and its already set to 0.

If you want to reinstall Firefox and think something is corrupt in the code and guts of Firefox delete the program files NOT the profile files. If you think it is a profile or settings issue use the Refresh option.

Your main Firefox should be the Release version Fx44, currently v44.0.2 that does not suffer from interference because of Security Software etc reducing the security! Keep that.

If you have installed Developer Edition you can keep that as well. By default DE is a separate browser and separate profile. I suggest you reinstall that but keep it separate.

• ^{Get help with Firefox Developer Edition}
• Please Do NOT, Sync with the Release
  See Recover lost bookmarks on Firefox Developer EditionNOT_option-2-turn-off-the-option-to-use-separate-profiles
  Please leave it with the default option to use a separate profile, and run at the same time as Firefox Release.

(I am not bothering to suggest a clean reinstall as you will have two separate installs) OK are you now able to run Firefox (Fx44) Release and DE at the same time ?

Now refresh DE

• Refresh Firefox - reset add-ons and settings

Does DE now work with secure sites ?

OK if that fails please do a comprehensive malware check using all of the tools mentioned in Troubleshoot Firefox issues caused by malware Full instructions:

Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• Anti-Rootkit Utility - TDSSKiller
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one. Windows 8 has antivirus built-in already.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History > Show All History" or "View > Sidebar > History") or via the about:permissions page.

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks, history, cookies, passwords, cache, and exceptions, so be cautious. If you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of the involved files.

If you revisit a 'forgotten' website then data from that website will be saved once again.

Thanks Cor-el, it isn't an issue with a specific site but with every site I have tried that has an https prefix.

John99, my system is free from malware, I run eset's full security suite and its pretty good and stopping almost all malware, I regularly run Malwarebytes just to find anything that has slipped through.

I do sync my profiles across several machines, all other versions of FF are working fine its only the one on the release builds of windows 10 that I'm having issues with.

So can you confirm you do have Firefox DE on the problem Windows 10 machine, and that you are able to run DE and Release together.

Please now try the Refresh on the Release {Note you will lose addons) Does that help ? If not do a clean reinstall as per our standard instructions that follow. Taking note it is the Program files and folder that need deleting.

As far as malware scans go it is still sensible to try with all the tools listed in the help article, and not just MalwareBytes and Eset.

Please check your Firefox version. And report what version it is. I note you did say you are using the latest version but could I ask you to double check that please. You may be stuck on Firefox 43 & that could explain the problem as Fx43 is too secure to allow use of Eset, if Eset is itself using a low grade insecure security certificate. If you are on Fx43, download and install Fx44 (soon Fx45) using another browser. Security of Fx44 has been relaxed to enable users to continue using such security software.

Clean Reinstall

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove your Firefox program files and then reinstall Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.

To do a clean reinstall of Firefox, please follow these steps: Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles.

So I now have 2 clean installs, one of firefox 44.0.2 and one of the developer edition. Neither of them will connect correctly to https sites. I'm now running windows 10 pro insider preview Build 14279.rs1_release.160229-1700. I'm able to access https sites with Microsoft edge and IE11 with now issues at all.

I will amend the title

• From: Unable to sign in to sync after reinstalling firefox
• To: Unable to use HTTPS after reinstalling firefox

As I understand it you now have two separate installs of Firefox, that both work with HTTP but not HTTPS, but it is ok with Edge.

I do not use Windows often, and do not know anything about "windows 10 pro insider preview Build ". Hopefully that is not causing your issues.

What may causes issues is security software either

• Because it does not recognise the new Firefox version as safe. See:
  Fix problems connecting to websites after updating Firefox
• OR it is using an insecure certificate, and Firefox does not consider it secure ( But you use Fx44 _{Unable to access secure (HTTPS) sites in Firefox 43}) How to troubleshoot security error codes on secure websites
• P.S. or as in post from guigs, outdated security software. With Eset AV specifically being one known culprit.

If reading those articles does not help, and no one else offers solution please post back again in a few days to bump your thread, because I haven't any other ideas..

I ran this by some firefox team members and was pointed to a similar bug https://bugzilla.mozilla.org/show_bug.cgi?id=1253755

It was concluded something with an antivirus was breaking the similar functionality that was broken in the bug mentioned. John99 did ask about the security software, can you confirm the antivirus if you are using one? If it is the case, eset may need to be updated.

Thank you!

Thank you John99 for all your help.

I'm running ESET ver 9.0.375.0 and get the same issue with it enabled or disabled.

"I ran this by some firefox team members and was pointed to a similar bug https://bugzilla.mozilla.org/show_bug.cgi?id=1253755"

It turns out this was the issue. I tried turning off and on the SSl/TSL as was done in the bug and this seems to have cured the issue. Thank you guigs.