@DVrandecic FYI the image is restricted

I've updated the description (mainly: it's only a problem in dark-mode browser/system themes) with new screenshots.
I'm not sure if the best solution is to either:

• create a new favicon that works well with any background? (We are currently using https://www.wikifunctions.org/static/favicon/wikifunctions.ico which I believe is derived from the SVG in https://commons.wikimedia.org/wiki/Category:Wikifunctions_logos )
• use CSS to switch between 2 different icons, e.g. @media (prefers-color-scheme: dark) might work?

In general: Ask a UI and/or graphic designer.
The simplest fix is probably doing what Wikipedia does, too: Put the logo on a white background. The more complex one is having a logo that works well as favicon on either background (Like phabricator’s). This will be tricky since the "W" is pretty flimsy (Same for Wikipedia’s W, thus their solution, I guess).

btw.: afaic one can use CSS for the favicon, but only if the icon is SVG (and thus the CSS will be the SVG’s CSS)

Suggest to split this in two issues just like one would do with a code-related issue. Solving that the outline looks bad has known fix (anti-aliasing and/or white background) whereas finding a favicon that looks less "W" like will be less trivial.

@Simulo Thanks for the nudge. I've split them properly now. I (should) know better than to merge semi-related issues; I blame semi-exhaustion! :)

Dark UI is not necessary. This is what it looks like on a tab in my Chrome with default UI:

Do we have the source file for the icon? Getting rid of the white outline in favor for a white background should be easy.

In T326094#9811474, @Simulo wrote:

Do we have the source file for the icon? Getting rid of the white outline in favor for a white background should be easy.

I believe the favicon should be reworked completely, see T343597#9811461.

I see the problems, but just flood-filling the background in white is a quick win.

How about this:

or this:

@DSmit-WMF It doesn't show me the last two – "File Not Attached" (you need to click "Attach file" in the "Referenced Files" list in the sidebar).

Have you considered reworking the favicon to keep only the lambda part (see the rationale in T343597#9811461)? The main problem of this logo is that it's hard to read. It's only readable as long as you have the white outline around the lambda (if the size of the format allows you):

Btw, I see the same problem with how it appears in Vector 2022 (on the right):