This site has an excellent collection of bookmarklets that help one overcome annoyances of some sites. This are simple and convenient tools that you can use when you get to one of those ugly sites. For example, you can quickly switch to black text over white background, disable marquee or blinking text, or make the textarea larger. You can even see passwords that are typed into password field as clear text.
All of these bookmarklets are advertised to work in both Netscape 7 and Mozilla. Most of them also work in MS Internet Explorer and Opera. Some even are applicable to Netscape 4. They are easy to save and use – simply drag and drop them to your bookmarks folder and then click while watching an annoying website.