I am installing Selenium right now and tutorials say, that i need Firebug. Unfortunnally on the download page (https://getfirebug.com/) it says:
The Firebug extension isn't being developed or maintained any longer. We invite you to use the Firefox DevTools instead, which ship with Firebug.next
Does it mean that i have to use Firefox DevTools to run Selenium now?
You don't always need firebug. Right clicking an element in firefox or chrome will provide you with an option to inspect an element. From there you can right click on the HTML to copy the xpath and CSS, as well as see an element's ID, name, class etc. The tools can be found by pressing ctrl+shift+i in both chrome and firefox.