Beginning in version 138, Firefox will offer an alternative to DLL injection for Data Loss Prevention (DLP) deployments in enterprise environments.

DLL Injection

DLL injection into Firefox is a topic we’ve covered on the Hacks blog before. In 2023, we blogged about the Firefox capability to let users block third-party DLLs from being loaded. We explained what DLL injection is, how we deal with problematic third-party modules, our about:third-party page, and our third-party injection policy. Earlier, in 2019, we released a study of DLL injection Firefox bugs in collaboration with Polytechnique Montréal. We return to this topic now, in the context of enterprise Firefox installations.

First, a reminder of what DLL injection is and why it continues to be problematic. DLL injection is the term we use to describe third-party Windows software injecting its own DLL module code into Firefox. Third parties develop DLLs for injecting into applications to extend their functionality in some way.…