https://en.wiktionary.org/w/index.php?title=Wiktionary:Feedback&oldid=47680828#Special:Search:
Please use the same quality settings for the Wiktionary favicon as the Wikipedia one, so Firefox can use it for the icon in the search box when you install the opensearch plugin.
Firefox has a size limit of 10kB for the icons (see https://dxr.mozilla.org/mozilla-central/rev/2d7b8b5dd174bd9db5894c6cb770e05f83e95ee3/toolkit/components/search/nsSearchService.js#101 ) Currently, the Wikipedia favicon is 2.7 kB (2,734 bytes) while the Wiktionary one is 15.1 kB (15,086 bytes). Just opening them in GIMP and re-exporting them, it appears Wikipedia is using 8 bpp, 1-bit alpha, 256-slot palette, without compression, while Wiktionary is using 32 bpp, 8-bit alpha, no palette, without compression. Just exporting Wikitionary's with the same setting as Wikipedia's gets it to 7.4 kB (7,406 bytes), safely under the limit.
The only change is to the alpha fade in the corners, but it's not really noticeable without enlarging, and Wikipedia's doesn't have it (might need to manually adjust them though).