some websites like twitter and wikipedia are not openning and in details "website is not encrypted" is written..please tell me solution of this problem..

You can try these basic steps in case of issues with web pages:

Reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

Clear the cache and cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

done all of this stuff but problm still not solved...

Doesn't Firefox load any content at all?

• Firefox > Web Developer > Page Source
• Tools > Web Developer > Page Source (Ctrl+U)
• right-click on a web page to open the context menu and select View Page Source

Does this only happen with these websites?

• https://support.mozilla.org/kb/web-pages-dont-load
• https://support.mozilla.org/kb/firefox+cannot+load+websites+but+other+programs+can

• http://kb.mozillazine.org/Error_loading_websites

yes..it happens with some websites like wikipedia and twitter...

same happens with page source...connection time out