Last modified: 2014-04-10 23:03:46 UTC
On my system, with Iceweasel (Firefox) 24.3.0, the effective body font size decreased. This appears to be due to the change in effective body font from DejaVu Sans to Nimbus Sans L. It seems the font family change means it's actually smaller despite the slight em bump.
I'm not sure what a feasible solution to this is, but I'm putting it here for tracking.
I'll attach screenshots from English Wikipedia, but the issue is also present in core (I compared wmf/1.23wmf19 to master (768c1872435a94ec936c982dd72cb0074b7ea6fc to verify it was present in core itself).
Created attachment 15052 [details]
English WIkipedia screenshot showing old fonts (2013-08-02)
Created attachment 15053 [details]
English WIkipedia screenshot showing new fonts with smaller effective size (2014-04-08)
Yes, Nimbus is the intended new font here.
The tradeoffs here are not obvious I think. Nimbus might end up a bit smaller, but the x-height is improved, which may on balance improve readability.
I'd be interested to see what the Chrome experience is too, since on Linux they tend to render slightly differently.
subjectively I think the Nimbus font is easier to read because of the greater difference i x-height to ascender height.
Per Jared's agreement that the advantage of Nimbus's improved x-height is worth it.