The default highlighted text color in OS X is blue, but you can change it to any color you want. Here is how you can change highlighted text color in OS X.
Wired Marker for Firefox allows you to permanently mark text on websites. The highlighted text will still be visible the next time you visit the site.
Whether you are in the browser, or typing a document in LibreOffice in Ubuntu, you can save highlighted text to the desktop with a simple drag and drop.
Researching on the Internet can sometimes be cumbersome. The Save Text To File extension for Firefox allows you to save highlighted text in any web page into a .txt file, then save it in any location on your hard drive.