Firefox is a great browser 'as it comes' but it really excels when it's used with 'add-ons'. The one you're referring to is Adblock Plus:
https://addons.mozill...US/firefox/addon/1865
Adblock Plus works by referring to a list of sites which send out ads, so it's important that it has an up to date list to refer to. For that reason you'll be asked, when you install Adblock Plus, to subscribe to a suitable list. (Don't be afraid of the word 'subscribe'. There's no payment involved!). I use 'Morpheus Rus List + EasyList' which works well for me. Once you've installed Adblock Plus (with a subscription) you should find that all of the ads at the bottom right of this screen have disappeared.
You might also want to add the British English dictionary, so that Firefox correctly spellchecks your posts here:
https://addons.mozill...US/firefox/addon/3366
Chris