Yesterday I installed the Safari extension "Glims" mainly as an easy means to set up DuckDuckGo as my main search engine. As as icing on the cake, Glims can show favicons next to tab labels. Now staring at my favicons, I refreshed my knowledge about them and found out that it is possible to have transparency in them. GraphicConverter, which I usually employ for this, does not allow transparency in favicons. But there's a simple workaround: Using GraphicConverter, convert to GIF, set transparency, and then save as favicon.ico. Lo and behold, transparency survives.