I want to write an addon/extension/script that allows me to hide specific parts of a website and remember these preferences. The next time I visit the website, this content should be hidden from me.Is there any way to do it?
What you are looking for are userscripts. userscripts.org has a collection of scripts for Greasemonkey on Firefox that may possibly work in Chrome or Opera.
If you want to write your own, here are some resources: