Add setting to anchor mode notifications

[adamlui]

. . .notifications in the corner are a bit much - it'd be nicer if they showed up near the bottom of the screen, as most of the notifications do from ChatGPT itself. However, this is a stylistic choice, and I'm glad they're easily visible regardless. . .

— Originally posted by Aria Dahl @ https://addons.mozilla.org/firefox/addon/chatgpt-widescreen/reviews/2228168/

[adamlui]

Added in 27d0add