One of the dirtiest secrets of the Internet is that it runs on ads for monetization. All of us who surf the web and use systems had lots and lots of free lunches because of advertisements being shown on web sites. The only difference to TV is that they are less obtrusive and you can choose to ignore or skip them (for now).
Self-righteous developers who do not quite grasp this dirty secret use all kind of tricks to remove adversiting from web sites they surf. This could be because of not wanting to support the corporate machine but also because of security reasons. Ad code on the internet is dire – it is built to support every possible imaginable environment and work around restrictions of setups – the ads need to show, no matter what.
Basically there are two extensions for Firefox that allow you to get rid of this potentially dangerous but definitely annoying code. Ad Block Plus specifically targets advertising and removes it and NoScript goes much further by blacklisting all scripts and asking you as a user to allow what you want to allow.
However, as mentioned in a discussion on SlashDot and commented in detail by Scott Schiller there has been a – quite ironic – incident lately.