When choosing a site-isolated process for a document loaded from a data: URL that was the result of a redirect, Firefox would load that document in the same…

When choosing a site-isolated process for a document loaded from a data: URL that was the result of a redirect, Firefox would load that document in the same process as the site that issued the redirect. This bypassed the site-isolation protections against Spectre-like attacks on sites that host an "open redirect". Firefox no longer follows HTTP redirects to data: URLs. This vulnerability affects Firefox < 114.