Firefox 121: New Notice System for Fullscreen Mode Transition

Summary

Multiple prompts and panels from both Firefox and the Android OS could be used to obscure the notification announcing the transition to fullscreen mode after the fix for CVE-2023-6870 in Firefox 121. This could lead to spoofing the browser UI if the sudden appearance of the prompt distracted the user from noticing the visual transition happening behind the prompt. These notifications now use the Android Toast feature. *This bug only affects Firefox on Android. Other operating systems are unaffected.* This vulnerability affects Firefox < 130.