I do not speak Russian, so I had to use Google Translate: "Does not control the browser.sessionstore.max_tabs setting. Because of what, no matter how much I put up the values of closed tabs, it was kept as much as indicated in browser.sessionstore.max_tabs"

No Firefox Add-on can control about:config settings. Mozilla does not allow it, but you can change the setting yourself manually. I mention this in the Add-on's options page, but it is possible that you were unable to read it because of the language barrier.