spin-off from bug 528531 comment 4: > For the slow mouseover feedback performance I've found that removing > display:block makes it a lot faster. Maybe we'll have to reimplement the > wrapping in JavaScript - mixing display:block with XUL doesn't seem to work > very well.

Comment on attachment 419291 [details] [diff] [review] patch Looks good and fixes the mouseover performance issues for me completely. >+ row = this.container.childNodes.item(Math.floor(++i / this._columns)); Out of curiosity, why .item() and not []?

I thought [] would complain if the index was >= the length, but apparently it doesn't.

(In reply to comment #2) > I thought [] would complain if the index was >= the length, but apparently it > doesn't. It should be a strict JavaScript warning. (e.g. document.createElement('label').childNodes[0])

I get the warning here: > document.createElement('label').childNodes[0] but not here: > var foo = document.createElement('label').childNodes[0]

Can you please file a layout bug, ideally with a testcase, on the slow-performance situation this worked around? It's not clear to me why display:block should be causing problems here.

(In reply to comment #6) > Can you please file a layout bug, ideally with a testcase, on the > slow-performance situation this worked around? It's not clear to me why > display:block should be causing problems here. filed bug 537037

Comment on attachment 419291 [details] [diff] [review] patch Requesting approval for an isolated change to visibly improve performance when interacting with the all-tabs panel. Only affects users who've toggled the hidden browser.allTabs.previews pref.