Earlier quoted context omitted.
I appreciate you answering, probably knowing you'd face some negative feedback. Saying "we should trust you, it's for a good reason" is what google and everyone else says. You'll be better off if you just end this. The loss of the fav icon is less important than keeping your credibility.
> is what google and everyone else says. Do Chrome, Firefox, or Safari do this? I would assume they do it on-device.
Chrome, according to my understanding, hardcodes a few favicon URLs for builtin search engines, and caches everything else on site visit. There's SQLite3 database named Favicons in your profile directory (e.g. on macOS it's ~/Library/Application Support/Google/Chrome//Favicons). Here's the schema:
CREATE TABLE meta(key LONGVARCHAR NOT NULL UNIQUE PRIMARY KEY, value LONGVARCHAR);
CREATE TABLE icon_mapping(id INTEGER PRIMARY KEY,page_url LONGVARCHAR NOT NULL,icon_id INTEGER);
CREATE TABLE favicons(id INTEGER PRIMARY KEY,url LONGVARCHAR NOT NULL,icon_type INTEGER DEFAULT 1);
CREATE TABLE favicon_bitmaps(id INTEGER PRIMARY KEY,icon_id INTEGER NOT NULL,last_updated INTEGER DEFAULT 0,image_data BLOB,width INTEGER DEFAULT 0,height INTEGER DEFAULT 0,last_requested INTEGER DEFAULT 0);
CREATE INDEX icon_mapping_page_url_idx ON icon_mapping(page_url);
CREATE INDEX icon_mapping_icon_id_idx ON icon_mapping(icon_id);
CREATE INDEX favicons_url ON favicons(url);
CREATE INDEX favicon_bitmaps_icon_id ON favicon_bitmaps(icon_id);
I haven't looked at Firefox and Safari but I assume they do something similar.