1327350 - Elements in scrollable area twitch up and down by 1 px when I scroll it to the beginning/end

Status: NEW

(Core :: Layout, defect, P3)

Description

[arni2033]

>>>   My Info:   Win7_64, Nightly 49, 32bit, ID 20160526082509
STR_1:  (originally encountered)
1. Open about:preferences#advanced -> "Update", click "Show Update History"
2. Drag scrollbar thumb in updated history to the bottom
3. scroll the dialog to the top (not to the very top) by scrolling mouse wheel
4. Hover mouse over link "Details"

AR:  The link twitches by 1px to the bottom
ER:  The link should stay still


STR_2:  (detailed)
[OF COURSE you won't reproduce it using STR_1, why do you ever complain about large number of steps?]
1. Extract "testcase 1" into a folder with short full name
2. Open .xul file in maximized non-e10s Firefox window
3. Open devtools toolbox, resize it so <dialog> element is 222.4px in height (according to box model)
4. Drag(!) scrollbar thumb on the page to the bottom.
5. Hover mouse over the scrollable area on the page, rotate mouse wheel up until you see history item
  "Nightly 50.0a1 (20160702030219)", but make sure you never scroll to the very top in this step.
6. Hover mouse over link "Details" in the history item "Nightly 50.0a1 (20160702030219)"
7. Hover mouse over the left button at the bottom of the page

AR:
 Step 6 - link "Details" teleports by 1px to the bottom
 Step 7 - Text labels "Nightly 50.0a1 (20160702030219)" and "Nightly 45.0a1 (20151209095500)"
          teleport by 1px to the bottom
ER:
 All said elements should stay still


Note:
 In Steps 5-7 you shouldn't hover any link or button unless the step says so.

Comment 1

[Timothy Nikkel (:tnikkel)]

And bug 1012752 didn't fix this? I noticed that you put this bug on the see also list of that bug, I would have expected it to fix this.

Comment 2

[Kartikaya Gupta (email:[e-mail])]

Bug 1012752 landed in August - arni, can you retest this one on a newer build? It should be fixed.

Comment 3

[arni2033]

I remember that I tested this after bug 1012752.
It makes no sense for me to test same bug again and again if nobody reproduced it on reported version.
"again and again" means that WHEN bug gets ignored for ~17 month, as Mozilla likes to do, then new people visit the bug and ask "is it still reproducible" each time. Mozilla should find an experienced tester and have a way to reliably reproduce the bug on their end (forever), rather than asking me.

Comment 4

[Timothy Nikkel (:tnikkel)]

(In reply to arni2033 [Please stop 'improving' Firefox] from comment #0)
> >>>   My Info:   Win7_64, Nightly 49, 32bit, ID 20160526082509
> STR_1:  (originally encountered)
> 1. Open about:preferences#advanced -> "Update", click "Show Update History"
> 2. Drag scrollbar thumb in updated history to the bottom
> 3. scroll the dialog to the top (not to the very top) by scrolling mouse
> wheel
> 4. Hover mouse over link "Details"
> 
> AR:  The link twitches by 1px to the bottom
> ER:  The link should stay still

I don't see the bug in a current aurora build.

Tried to reproduce in the 2016-05-26 nightly using mozregression, but no updates have been installed so there is nothing to scroll. So I manually downloaded the nightly for that date and ran it on a profile that has had updates, but that still doesn't show any updates. So to try to reproduce this in 2016-05-26 build I'm guessing I would have to install a builder older than 2016-05-26 and then somehow convince the mozilla update server to send me the 2016-05-26 build (which I think is impossible).

> 
> STR_2:  (detailed)
> [OF COURSE you won't reproduce it using STR_1, why do you ever complain
> about large number of steps?]
> 1. Extract "testcase 1" into a folder with short full name

There is no attachment in this bug.

So we've got no way to try to reproduce this bug, there's no way for someone other than the reporter to verify if this is fixed or still around.

Comment 5

[castiel743]

Attachment: testcase 1 - bug 1327350.zip

>>>   My Info:   Win7_64, Nightly 53, 32bit, ID 20170104030214 (2017-01-04)
It was rather logical to ask for attachment in the first comments then...
Luckily, I have a testcase that reproduces the issue as reported, on the "latest" Nightly.
You'll need one additional step:
0. Set HiDPI level in your OS (or in Firefox (pref "layout.css.devPixelsPerPx")) to 125%

Comment 6

[Botond Ballo [:botond]]

(In reply to castiel743 from comment #5)
> Created attachment 8824750 [details]
> testcase 1 - bug 1327350.zip
> 
> >>>   My Info:   Win7_64, Nightly 53, 32bit, ID 20170104030214 (2017-01-04)
> It was rather logical to ask for attachment in the first comments then...
> Luckily, I have a testcase that reproduces the issue as reported, on the
> "latest" Nightly.
> You'll need one additional step:
> 0. Set HiDPI level in your OS (or in Firefox (pref
> "layout.css.devPixelsPerPx")) to 125%

First, a note for anyone else trying to reproduce this, opening a local XUL file requires first setting the undocumented pref "dom.allow_XUL_XBL_for_file" to true.

That said, I tried following STR_2 (from comment 0) for this page, and found that the page did not have a scrollbar (i.e. was not scrollable), even after decreasing its height by opening and resizing the devtools.