I don't get this error on Chrome or Firefox and I use them on desktop and mobile. Try clearing your browser's temporary files including browsing history, cookies and cached images. On Firefox, press Ctrl + Shift + Del or on your keyboard and this window pops up.
Note: if you clear "Cookies" then you'll be logged off of any web-sites you've used like Gmail, Outlook, Terb, etc. You will need to type your username and password again for those sites. Luckily, all browsers stores these for you. In the Firefox settings, look for the Login and Passwords section and clicking the Saved Logins button. When you clear cookies, any site you've customized will go back to its default state. So you will have to customize those sites again. This process is the similar in all browsers like Edge and Chrome.
If this process doesn't work, then you can also try following these steps from this article:
Firefox shows you a warning page about a potential security risk when you try to connect to a secure site but your connection is not secure.
support.mozilla.org
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Corrupted certificate store
You may also see certificate error messages when the file in your profile folder that stores your certificates cert9.db has become corrupted. Try to delete this file while Firefox is closed to regenerate it:
Note: You should only perform these steps as a last resort, after all other troubleshooting steps have failed.
- Open your profile folder:
- Click the menu button
, click Help and select More Troubleshooting Information. The Troubleshooting Information tab will open.
- Under the Application Basics section next to Profile Folder, click Open Folder. Your profile folder will open.
- Note: If you are unable to open or use Firefox, follow the instructions in Finding your profile without opening Firefox.
- Click the Firefox menu
and select Exit.
- Click on the file named cert9.db.
- Press Delete.
- Restart Firefox.
Note: cert9.db will be recreated when you restart Firefox. This is normal.