1148391 - Tapping the bottom of the screen will make the reader mode toolbar bounce up and down

Status: RESOLVED FIXED

(Firefox for Android Graveyard :: Reader View, defect)

Description

[Teodora Vermesan (:TeoVermesan)]

Tested with:
Device: Nexus 5 (Android 5.0)
Build: Firefox for Android 39.0a1 (2015-03-26) and Firefox for Android 38.0a2 (2015-03-27)

Steps to reproduce:

1. Open http://goo.gl/0fdkDo and enter reader mode 
2. Go to the bottom of the page (the reader mode toolbar disappears)
3. Tap on the bottom of the screen to invoke the toolbar

Expected results:
- The reader mode toolbar slides on the screen.

Actual results:
- The reader mode toolbar appears but is not fixed to bottom of content window
- Tapping on the screen and will display the toolbar fixed to the bottom
- Tapping once again the screen will bounce up the toolbar

Please see the following video:
http://youtu.be/oRzJASXixAg

Regression from  Bug 998031 - Reader Mode toolbar should scroll in and out instead of fading

Comment 1

[:Margaret Leibovic]

Vivek, are you also interested in taking this one? This is worse than bug 1145567 IMO, but I'm not sure what's causing this.

Comment 2

[Vivek Balakrishnan[:vivek]]

Thank Margaret, 
I'll take it.

Comment 3

[:Margaret Leibovic]

Talked with Vivek about this on IRC, I'm going to help investigate.

Comment 4

[:Margaret Leibovic]

This is a bug with the platform, not specific to about:reader. I made a testcase to demonstrate:
http://people.mozilla.org/~mleibovic/test/position-fixed.html

This works as expected on desktop.

I can try to come up with a workaround that we can uplift to beta, but this really should have a platform fix.

blassey, who's the right person to look into this?

Comment 5

[:Margaret Leibovic]

So it looks like this issue is definitely related to the dynamic toolbar. If you scroll *almost* to the bottom, such that the dynamic toolbar doesn't become visible, you don't see this issue. But as soon as the toolbar is visible, we get this weird mis-positioned footer.

Comment 6

[:Margaret Leibovic]

kats, do you have any idea what might be going on here? Would you be able to look into this, or know someone else who could?

Comment 7

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

I spent some time staring at the code and it's not obvious to me why this is happening. Best guess is that both the viewport margins and the fixed-position margins are getting applied, which is too much. It probably also has top do with the fact that when we are at the bottom of the page and the toolbar is visible, it is actually overlapping the layerview rather than pushing it down. But I'm not really sure. Wes or snorp might be able to dig into this but frankly at this point the code is more or less unowned, unmaintained, and buggy. We should try to explore new UX paradigms around this, preferably something that will also be more compatible with the C++ APZ code so that the transition to that will be easier.

Comment 8

[:Margaret Leibovic]

I just spent a bit of time trying to see if there's a way to come up with some JS/CSS hacks to work around this problem, but I'm at a loss for what to do. A few things I tried included triggering a reflow when we're at the bottom of the page (since somehow the toolbar repositions itself correctly if you inspect it with the devtools), and playing around with the CSS padding/margin at the bottom of the body. The closest I came to a solution was changing the bottom values when we're scrolled to the bottom of the page, but it seems like window.scrollY isn't giving me the right values, so my code thinks we're at the bottom of the page even when we're not.

This looks really shitty, and I don't want to ship this to users, so I'm open to any ideas other people have.

Comment 9

[:Margaret Leibovic]

Attachment: Hack: Account for broken fixed position margins at bottom of about:reader

This fixes the problem when we're scrolled all the way to the bottom of the page, but it mispositions the toolbar if we're scrolled to slightly above the bottom of the page.

Comment 10

[:Margaret Leibovic]

I think we just need a platform fix for this.

Comment 11

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

This is fixed by bug 1180295.

Comment 12

[Teodora Vermesan (:TeoVermesan)]

Still reproducible with Firefox for Android 42 Beta 1 using Samsung S6 (Android 5.1)