We need this button!! Someone from Firefox team please make this happen.
(menubar File => Work offline)
It applies to the whole browser, not the current tab. But good enough.
1. starts by suggesting devTools, which is simple, elegant, and wrong.
2. improves by suggesting the "Work Offline" menu option of the File menu, which is hidden by default on both Windows and Linux, and also wrong.
3. improves to a state of minimal functionality with implicitly ordered steps to use Private Browsing, Offline Mode, and confidential file "upload." And, I guess, always remembering to close all private browsing windows upon completion?
I'll rankly speculate f this ever caught on, 25% of users will forget to check offline mode until after they have finished editing their confidential document, 40% will leave a stray Private Browsing window open at all times, 10% will accidentally continue doing all their browsing in the same Private Browsing window, and 1% will somehow paste their private GPG keys in the query string of the URL.
Websites are not meant to not use the internet.