Many mac os X users are complaining of slowness of the button when trying to remove very small amounts of history. We need to profile this and investigate what happens when we have a deep history that we are forgetting some significant part of (but not all) which will likely have the worst performance characteristics. Dolske, please find someone to profile this Tracy, Can you (or someone you find) test this on a mac with a large profile of history and see what you get?

cc'ed some beachballers

I will investigate in the morning, but is it possibly related to the way Windows are closed per https://bugzilla.mozilla.org/show_bug.cgi?id=1088137#c8 ?

I had asked Toby earlier today if he could shed any light on his experience. This is what he sent: "The site was na.lolesports.com, which shouldn't be anything too unusual. It was a redirect from just lolesports.com. I just did an hour history clear in Aurora and got a beachball for about the same length." (5 seconds)

Note: I reported this on a linux computer (ubuntu 14.04 lts, 64bit, hdd, lenovo w520)!

(On Mac 10.9.4) I couldn't reproduce with a large history. However loading just over 100 tabs, then Forget last five minutes did trigger sluggishness to close the window, beachball and UI glitchiness on building new window. The entire process took about 5 seconds as reported.