I see this issue on: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.1b3pre) Gecko/20090123 Shiretoko/3.1b3pre i'm on a long bugzilla list of bugs, i scroll up or down with the mouse wheel or the keyboard up/down keys (does not happen if i drag it to a position). The grippy appears and disappears intermittently. Notice this does not happen on short pages, seem to happen only when the scrollbar grippy is at minimum size. i recorded a small video to show the issue: http://www.bonardo.net/scrollbar/ I'm not sure this is the right component for scrollbars, but couldn't find a better one :\
If these are native-drawn scrollbars, then it's probably the native theme code, although not definitely.
Or was this a recent regression? If so, maybe more likely layout.
it was working in 3.0.x, i should try to find a regression range
works: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.1b1pre) Gecko/20080917034815 Minefield/3.1b1pre does not work: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.1b1pre) Gecko/20080918073230 Minefield/3.1b1pre regwindow could be: http://hg.mozilla.org/mozilla-central/pushloghtml?startdate=2008-09-17+03%3A48%3A15&enddate=2008-09-18+07%3A32%3A30
not sure I've seen this, but I've encountered page which wouldn't scroll using XP Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2a1pre) Gecko/20090621 Minefield/3.6a1pre (.NET CLR 3.5.30729)
20160502172042 Mozilla/5.0 (Windows NT 6.0; rv:46.0) Gecko/20100101 Firefox/46.0 20160509040557 Mozilla/5.0 (Windows NT 6.0; rv:49.0) Gecko/20100101 Firefox/49.0 I tested on Windows Vista x86 with FF latest release 46.0 and latest Nightly 49.0 on a long bugzilla list of bugs and I can't reproduce the issue. Please retest this on the latest Firefox version and see if you can reproduce the problem.