Some developers create extensions that distribute malware or show users pop-up ads, flashing banners, and other intrusive advertising. That is why Yandex.Browser allows you to install extensions only from Chrome Web Store and Opera Add-ons where extensions are checked.
If you install an extension from another website, the browser will disable it immediately after installation and inform you of this. If you trust the source, you can enable the extension for a single session by clicking Enable in the upper-left corner of the window:
When you click OK in the window, the extension from an untrusted source is disabled. If you want to enable the extension later, you can do this in the browser settings: