LS cookies are mostly flash Cookies (.LSO files, Local Shared Objects) that websites like Megavideo, Youtube, Veoh, or such (streaming media sites) leave on your computer. They can be up to 300mb I think (Biggest one I had was about 200mb if I remember correctly). When you clear all data on firefox/chrome/opera, it doesn't get rid so Better Privacy (It's the real name of the addon) deletes them.
Some websites use them for time limits. I can usually skip the 30 minute wait and watch videos immediately after the 72 minute limit deadline on Megavideo.
It's a handy addon that also saves me a lot of space.
More info here
http://en.wikipedia.org/wiki/Local_Share...ct#Storage
LSOs can be used by web sites to collect information on how people navigate those web sites even if people believe they have restricted the data collection.[4] More than half of the internet’s top websites use LSOs to track users and store information about them.[5] There is relatively little public awareness of LSOs, and they can usually not be deleted by the cookie privacy controls in a web browser.[5] This may lead a web user to believe a computer is cleared of tracking objects, when it is not.[5]
Several services even use LSOs as surreptitious data storage to reinstate traditional cookies that a user deleted, a policy called "re-spawning" in homage to video games where adversaries come back to life even after being "killed". So, even if a user gets rid of a website’s tracking cookie, that cookie’s unique ID will be assigned back to a new cookie again using the Flash data as "backup." [6] In USA, at least five class-action lawsuits have accused media companies of surreptitiously using Flash cookies.[7]
In certain countries it is illegal to track users without their knowledge and consent. For example, in the UK, customers must consent to use of cookies/LSOs as defined in the “Guidance on the Privacy and Electronic Communications (EC Directive) Regulations 2003”:[8]
Cookies or similar devices must not be used unless the subscriber or user of the relevant terminal equipment:
is provided with clear and comprehensive information about the purposes of the storage of, or access to, that information; and
is given the opportunity to refuse the storage of, or access to, that information.