This bug was filed from the Socorro interface and is report bp-169ff542-249e-49c2-933d-4920b0170531. ============================================================= There are reports of this on Window NT and Mac OS X. It just started with the latest Nightly, 55.0a1, 20170531030204. I crashed with only about:newtab open. The browser seemed to crash when I clicked away from the window (click on desktop), but that may have been coincidental. I haven't reproduced the crash yet. One install on Mac has already submitted two reports.

discovered reliable STR's 1) Open a new tab (about:newtab, command+T or "+" in tab bar) 2) ensure the window is small enough that the vertical scroll bar is present 3) click on the scroll bar tested result: CRASH expected result: scroll bar is clickable for mouse sliding note: mouse wheel scrolling and touch pad scrolling of about:newtab works fine.

I haven't seen this on regular web pages. Seem to be reproducible only on a variety of about: pages.

Thanks for the STR, I am able to repro.

There was a latent bug in nsBaseWidget::StartAsyncScrollbarDrag(), where a uint64_t value (the roots layers ID) was temporarily coerced into a 32-bit variable, losing the top 32 bits. This latent bug was exposed by the recently landed bug 1366915, which changed the way layers IDs are allocated to make use of the top 32 bits all the time.

Comment on attachment 8873120 [details] Bug 1369074 - Store the layers id in a variable of the proper type (uint64_t) in nsBaseWidget::StartAsyncScrollbarDrag(). https://reviewboard.mozilla.org/r/144592/#review148446

Pushed by bballo@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/8709ce04de16 Store the layers id in a variable of the proper type (uint64_t) in nsBaseWidget::StartAsyncScrollbarDrag(). r=kats

Today's Nightly update no longer crashes clicking the scrollbar on about: pages.