Hi! I attached a short .mov-file (8 seconds). Please look at the end of the bookmarks toolbar after closing the customization tab. Do you see the additional bookmark for a very short moment?

I don't think this is fixable without rearchitecturing how the bookmarks toolbar overflow works. It relies on overflow events, and to get those, it needs to just display everything. Marco, is that impression correct?

yes, and honestly I don't see how we may rearchitecture overflow without using overflow events... What we may do here is add an overflow buffer that collects overflow/underflow events and delays them for a while to avoid flickering, by killing overflow/underflow that happen in a short timeframe.

though, in this case we show elements and then we hide them, so that wouldn't work. we could hide buttons so that they take up the space for overflow to happen, and then unhide them later

(In reply to Marco Bonardo [:mak] from comment #3) > though, in this case we show elements and then we hide them, so that > wouldn't work. we could hide buttons so that they take up the space for > overflow to happen, and then unhide them later Fair point, we could get the 'unitialized' state have visibility: hidden on all the items instead of nothing, and presumably the overflow event would still happen?

it's worth a try...