Web dev here. It enforces the original markup and code from a server to be the markup and code that the browser interprets and executes, preventing any post-loading modifications.
That sounds a bit dry, but the implications are huge. It means:
These are just a few things off the top of my head. There are endless and very dangerous implications to WEI. This is very, very bad for the web and antithesis of how it’s supposed to be.
TBL is probably experiencing a sudden disturbance in the force.
Well whaddaya know, you get what you pay for.
That being said, companies should be legally obligated to provide security patches for a minimum number of years.