Hi,

One reason could be that there are no extensions installed in the browser. Please note that extensions are different from plugins like Flash and Java.

This can also sometimes happen if extensions are installed from outside of the official Mozilla AMO. Add-ons installed from external sites may entirely skip the Firefox Tools (or Alt + T) > Add-ons interface.

Add-on already installed please see http://s017.radikal.ru/i444/1112/7c/5515912ad9c3.jpg and i know how to install new add-on or how to found installed add-on. my question: i cant see Installed add-on in "Add-on Manager".

Sorry, I missed that.

Please try this: Help (or Alt + H) > Troubleshooting Information > Open Containing Folder. After the folder opens exit Firefox and delete the three files named extensions.ini, extensions.log and extensions.sqlite and start Firefox.

Please also see this.

Thank you! Problem solved!