hello lormand, please try to reset firefox and see if this can address the issue...

Something changed your home page. If you prefer the built-in home page, you can delete the ominent address in the following dialog, and use about:home instead.

• Startup, home page, tabs, and download settings
• How to set the home page

But... this might not stick if whatever switched your home page is still on your computer. Please also check:

(1) user.js file

This is a file that Firefox reads at startup which overrides your previous session settings. To remove this file, see the steps in this article: How to fix preferences that won't save. Note: If windows does show the .js on files like prefs.js, sessionstore.js, and user.js, you can turn off the hiding of file extensions using the methods in this article: http://support.microsoft.com/kb/865219.

(2) Windows Control Panel, Uninstall a Program

Click the "Installed on" column heading to bring the most recent infections, I mean additions, to the top. If you recently installed some free software, it may have been bundled with whatever is responsible for changing your home page. Try to remove unwanted software here.

And... hopefully that will cure it! If you want to mop up a bit more, check out the cleanup tools other Firefox users have found helpful, in this article: Troubleshoot Firefox issues caused by malware.

Set firefox as my home page; Now, every time I try to type in a website (yahoo or (Mozilla firefox), I receive this message:

This Connection is Untrusted

You have asked Firefox to connect securely to login.yahoo.com, but we can't confirm that your connection is secure.

Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified. What Should I Do?

If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue.

first please make sure that the date & time is set correctly on your system.
if this doesn't solve the issue (or it is already set properly), could you tell us which error code is shown under technical details on the error message and when you inspect the certificate which issuer information it does contain (see screenshot)?

"This Connection is Untrusted" error message appears - What to do

got me to the firefox homepage, but now I get this message and am unable to access yahoo or any other sites:

This Connection is Untrusted

You have asked Firefox to connect securely to login.yahoo.com, but we can't confirm that your connection is secure.

Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified. What Should I Do?

If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue.

Seems to be a perpetual loop because even if I accept the risks, it still won't allow me to access sites. Arggh.

lormand, in order to give you a targeted reply, please provide the two pieces of information requested:

• what is the error code shown under Technical Details on the ""This Connection is Untrusted"-page
• when you inspect a certificate like described in the screenshot above, what is its issuer information?

What does it say under the Technical Details?

Hi lormand, I don't know whether you saw philipp's post here: https://support.mozilla.org/en-US/que.../985749#answer-531348.

The reason we're asking you to look at that "Issued by" information is recently many Firefox users are running into problems with their security software filtering feature. In order to filter secure connections (HTTPS URLs), the security software presents a fake certificate to Firefox so it can intercept and stand in the middle of the secure connection. To have Firefox trust these certificates, you may need to do something such as import a root certificate, or click something in your security software's settings.

Of course, the problem also could be caused by spyware.

The kind of issuer you might find is:

• Name associated with your security software, such as ESET, BitDefender, etc.
• Sendori (indicates unwanted software from Sendori)
• FiddlerRoot (indicates unwanted software named similarly to BrowserSafeguard, BrowserSafe, SafeGuard)
• Something else

Technical Details

login.yahoo.com uses an invalid security certificate. The certificate is not trusted because no issuer chain was provided. (Error code: sec_error_unknown_issuer)

time and date are correct

don't understand what I need to do

this screenshot should show the process how you can obtain the "issued by" information contained in the certificate:

Technical Details

login.yahoo.com uses an invalid security certificate. The certificate is not trusted because no issuer chain was provided. (Error code: sec_error_unknown_issuer)

I understand the risks:

If you understand what's going on, you can tell Firefox to start trusting this site's identification. Even if you trust the site, this error could mean that someone is tampering with your connection.

Don't add an exception unless you know there's a good reason why this site doesn't use trusted identification.

Certification Viewer: “login.yahoo.com” Could not verify this certificate because the issuer is unknown. Issued to Common Name (CN) login.yahoo.com Organization (O) DO_NOT_TRUST Organizational Unit (OU) Created by http://www.fiddler2.com Serial Number B2:F6:3C:0E:37:C4:38:A6:44:31:2E:53:92:7F:C5:A6

Issued by Common name (CN) DO_NOT_TRUST_FiddlerRoot Organization (O) DO_NOT_TRUST Organizational Unit (OU) Created by http://www.fiddler2.com

Validity Issued On 1/30/2014 Expires On 1/29/2024

Fingerprints SHA1 fingerprint: 2E:CB:D5:A6:1F:21:44:B2:86:1C:BE:C7:67:0B:6B:51:2C:47:81 MD5 Fingerprint EC:B6:3E:23:04:49:22:C4:AE:1C:27:37:0E:F9:67:7D

unfortunately the do_not_trust certificates might be a sign of unwanted software present on your pc that is intercepting secure network traffic. please go into the system control panel and uninstall programs like BrowserSafeguard, BrowserSafe, SafeGuard or other software that sounds suspicious and didn't get installed by you intentionally.
_{reference: https://support.mozilla.org/en-US/questions/982532#answer-520145}

afterwards, run a full scan of your system with different security tools like the free version of malwarebytes & adwcleaner.

Troubleshoot Firefox issues caused by malware

This is new to my computer:

microsoft Visual C++ 2008 Redistributable - x64.9.0.30729.17 dated 2.1.2014

There are other Microsoft Visual C++ 2008 Redistributable with other numbers listed. Should I remove the one dated 2014 also?

Sounds that you have installed software that included installing the Fiddler network proxy.

• http://www.fiddler2.com/fiddler2/

nope, didn't install a fiddler program

Hi lormand, does that date correspond with any other suspicious items? You can click the "Installed on" column heading to group together the install dates and get a better idea of what might have been bundled together.

Mozilla Firefox 2.7 2/7/2014 Mozilla Maintenance Service 2/5/2014 Adobe Flash Player 12 Plug-in dated 2/5/2014 microsoft Visual C++ 2008 Redistributable - x64.9.0.30729.17 dated 2.1.2014

the software doesn't have to be installed recently - it probably has put its fake certfificate into the firefox certificate store, which was removed again when you have reset the browser. so it might have been going on for a while unrecognized...