Web addresses should be typed using the \url command. This is provided by the url package, amongst others. Provided there are not long strings of letters in the address then these will break over lines without further action.
Different formatting of the footnote may be provided by options from the footmisc package:

\documentclass{article}
\usepackage{url}
\usepackage[flushmargin]{footmisc}
\begin{document}
Some text\footnote{Some interesting homepage on the web. Accessible at
\url{http://www.w3.org/standards/webdesign/htmlcss} [12th December,
2009]. More text to demonstrate the shape of the footnote paragraphs.
More text to demonstrate the shape of the footnote paragraphs.
More text to demonstrate the shape of the footnote paragraphs.} and
more text.
Some text\footnote{Some interesting homepage on the web. Accessible at
\url{http://www.w3.org/standards/webdesign/htmlcss} [12th December,
2009]. More text to demonstrate the shape of the footnote paragraphs.
More text to demonstrate the shape of the footnote paragraphs.
More text to demonstrate the shape of the footnote paragraphs.} and
more text.
\end{document}
urlpackage and writing these as\url{http://www.w3.org}. Then if there as still problems, look at other questions here about breaking url's, e.g. http://tex.stackexchange.com/q/15653/15925 – Andrew Swann Dec 29 '13 at 13:46Edit: \usepackage[hyphenbreaks]{breakurl} didn't help as well.
– UserSoUndSo Dec 29 '13 at 13:58\footnote{Title. Link \url{http://www.w3.org} [Date]}– Andrew Swann Dec 29 '13 at 14:17
– UserSoUndSo Dec 29 '13 at 14:30Undefined control sequence. <argument> ... Is Web 2.0. Verfügbar unter: \url {http://www.ttivanguard.co... l.50 ...dc05session4003.pdf}. [27. Dezember 2013]} . The control sequence at the end of the top line of your error message was never \def'ed.[etc]\urlcommand is not defined, then you need a\usepackage{url}in your preamble. – Andrew Swann Dec 29 '13 at 14:32