Features:

Ensures pages do not display your personal information, EVEN while and before loading.
Prevents changes to the pages from showing your personal information.
Ability to specify any string as personal information.
Warns users if a page is not fully supported by the extension, to prevent them from accidentally leaking their information.

Known Issues:

Must be manaully updated when new unsupported sites are reported.
Doesn't support all sites
Tab title is still visible during load, leaking personal information contained in the title.

Github: https://github.com/AidanSpeakss/streamer-mode-for-firefox