this connection is untrusted keep appears in youtube ,when i open youtube the advertisement become this error msg ,and cannot click ,no option. when i start firefox, keep pop up checking your add-ons msg ,i don't know how to disable it , it annoying.i don't know it have a connection or not,but all the problem appears after i install avast free antivirus,i use firefox 18.0.1.
Does it work if you use a normal http link?
Clear the cache and the cookies from sites that cause problems.
"Clear the Cache":
"Remove Cookies" from sites causing problems:
Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).
thank first.the youtube problem is solve,but the checking your add-ons still pop up whenever i start firefox.i already clear the cache and cookies,try to start firefox in safe mode and check the default theme, but all these don't seem to solve my problems.and firefox always open up with two tabs along with 'welcome to firefox' ,how to disable it?
Note that https://www.youtube.com/ has mixed content (i.e. some content comes via an unencrypted http connection).
You can see this in the "Web Developer > Web Console" (Ctrl+Shift+K) as lines marked in red text with [Mixed Content] added.
You can check for problems with preferences and try to rename or delete the prefs.js file and possible numbered prefs-##.js files and a possible user.js file to reset all prefs to the default values.
Create a new profile as a test to check if your current profile is causing the problems.
See "Creating a profile":
If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.