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For some reason anything that I pull up using Firefox is getting blocked and I get a security warning, even this support site was blocked.

struong68
struong68

Everything I pull up (even sites I have used many times before and use daily are getting blocked on Firefox). I try to go to Advanced settings and add an exception or allow certain sites but I can't. I am not sure what happened but the one site I currently used and the only one I was able to "allow" is our Retail POS system but it also now shows up a little wonky. None of the icons are showing up and everything looks a little "off" as far as the layout, buttons, etc. Not sure what changed. I checked to see if my version of Firefox was updated and it shows there are no updates available for me to run. I have to now use Chrome for everything, which is not my preferred browser. What else can I check to see why all of a sudden all sites are showing up with message on Firefox stating "Your Connection is not secure" with this Error code: MOZILLA_PKIX_ERROR_MITM_DETECTED

Everything I pull up (even sites I have used many times before and use daily are getting blocked on Firefox). I try to go to Advanced settings and add an exception or allow certain sites but I can't. I am not sure what happened but the one site I currently used and the only one I was able to "allow" is our Retail POS system but it also now shows up a little wonky. None of the icons are showing up and everything looks a little "off" as far as the layout, buttons, etc. Not sure what changed. I checked to see if my version of Firefox was updated and it shows there are no updates available for me to run. I have to now use Chrome for everything, which is not my preferred browser. What else can I check to see why all of a sudden all sites are showing up with message on Firefox stating "Your Connection is not secure" with this Error code: MOZILLA_PKIX_ERROR_MITM_DETECTED

Chosen solution

Please go through your Extensions and turn off any scanners.

There is security software like Avast/AVG, Kaspersky, BitDefender and ESET that intercept secure connections and send their own certificate. If you are running any of the above software please check their community forum for a work around to apply settings.

i'd recommend to turn off the https scanning functionality within their settings, like it's described for below :

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Shadow110
Shadow110

Chosen Solution

Please go through your Extensions and turn off any scanners.

There is security software like Avast/AVG, Kaspersky, BitDefender and ESET that intercept secure connections and send their own certificate. If you are running any of the above software please check their community forum for a work around to apply settings.

i'd recommend to turn off the https scanning functionality within their settings, like it's described for below :

jscher2000 - Support Volunteer
jscher2000 - Support Volunteer
  • Top 10 Contributor

Another article for the "MITM" issue is this one: How to troubleshoot security error codes on secure websites.

jscher2000 - Support Volunteer
jscher2000 - Support Volunteer
  • Top 10 Contributor

struong68 said

... the only one I was able to "allow" is our Retail POS system but it also now shows up a little wonky. None of the icons are showing up and everything looks a little "off" as far as the layout, buttons, etc.

By the way, please don't create exceptions for sites that handle sensitive data. This error is a red flag that there is an impostor in your connection -- MITM = "man in the middle." It could be an authorized filter or it could be malware. It's always best to chase that down before deciding to make exceptions.