Created attachment 832952 [details] Comparison of views.png User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0 (Beta/Release) Build ID: 20131025151332 Steps to reproduce: Upgrade from Version 17.0.8 to 24.0 Backtracked versions to find first appearance in 22.0b1 Comparison of views are from 21.0b1 and 22.0b1 Actual results: When using Littlebird theme, spacing between folders and messages increased to standard spacing of default theme. Expected results: Spacing should have been unchanged.
Are you using the 125% in the Windows Control Panel > Display settings? If yes, that's now scaling UI icons as well (and those look scaled to me). Try changing layout.css.devPixelsPerPx from -1.0 to 1.0 in Thunderbird (Options > Advanced > General > Config Editor).
Yes, I'm using 125% in Display settings, and changing layout.css.devPixelsPerPx to 1.0 certainly makes the icons smaller, but it makes everything else smaller too. The icons in this theme are normally only about 75% to 80% the size of default icons (I would need to check with the theme developer for actual sizes) but whatever has changed makes them the same size as the icons in the default theme. Icons from the same theme remain the designed size in other places (e.g. toolbars). I've checked by changing to 100% in Display Settings, the designed icon sizes are not being used in these panes.