I learned recently that some people avoid blocking/muting users on #ao3 because they can't stand the notification bar that is visible at the top of every page if you do
I am here to bring good news: this is fixable, using site skins! Even if site skins intimidate you, it's an easy copy-paste situation. All you need to do is create a site skin, paste 3 lines of text into the css field, save it, and apply it as your standard site skin.
Or if you use a custom skin (eg one of official ao3 skins, or other public skins) you can duplicate the skin, saving it as your own, and then edit it, and add the same 3 lines to the code along with all the other css that's already there. And then the fix will be implemented as part of your usual skin.
Here's what you need, these 3 lines. Including the third line with the closing curly bracket is important! and then you're good and will never see the notification banner about mutes/blocks again when you're logged in :)
p.muted.notice {
display: none;
}