in bug 1187203, comment 28, `-moz-appearance: -moz-gtk-info-bar` was added to RSS feed CSS on linux; this messed up the borders for #feedHeaderContainer in the RSS preview interface ... In the theme I use ("TraditionalOk" in Mate Desktop), the side borders are missing, the bottom border color doesn't match the border color for #feedBody, and the border-radius declaration isn't respected (see comparison screen capture). Interestingly, Inspector shows the missing styles as active, however, I can only see them when I disable `-moz-appearance: -moz-gtk-info-bar` regression range: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=22c34579ae0720e7d3dc39a22b9d33f13bc0198b&tochange=8a6045d14d6bd348a3b5bfeb55a9321e680cc93e specifically, I believe it's: https://hg.mozilla.org/mozilla-central/rev/ea072f95e28e

Ty for the bug report and the regression range.

Karl, can you please take a look since Andrew isn't available these days?

Thanks for the detailed report, but I think this is wontfix because the intention is to draw the notification element like a native info bar, and I think this is what was intended from this in TraditionalOk 3.18.3: GtkInfoBar:last-child, .info:last-child, .warning:last-child, .question:last-child, .error:last-child { /* only apply a border on the last infobar if * there's more than one packed in */ border-bottom-width: 1px; border-style: solid; } .info > * { background-color: @info_bg_color; color: @info_fg_color; border-color: darker(@info_bg_color); } -moz-appearance typically overrides border and background in UA style sheets. (Oddly "Info Bars" in gtk3-demo 3.18.9 does not show the backgrounds, presumably because the child of .info is a GtkRevealer (since 3.10), which does not draw a background, in that version of GTK.)