1634553 - In Facebook "Hide Ad" UI for sponsored posts, the "why did I see this ad" dialog has unnecessary scrollbars

Status: NEW

(Core :: Layout: Scrolling and Overflow, defect, P3)

Description

[Daniel Holbert [:dholbert]]

Attachment: screenshot of the bug (showing the unnecessary scrollbars)

STR:

1. Be logged in to Facebook (in Firefox on Desktop)

2. Scroll through your news feed until you find a sponsored post (there'll be a "Sponsored" label at the top left)

3. Click the "..." and choose "Hide this ad"

4. Choose one of the provided reasons for hiding (e.g. "Irrelevant") and click OK/Next (or whatever the button is labeled)

5. On the "Ad Hidden" dialog, under "Other steps you can take", choose "Why did I see this ad?"

ACTUAL RESULTS:

• The "Why did I see this ad" dialog appears with unnecessary scrollbars that only let me scroll a few pixels.
• I can tell they're unnecessary because if I use devtools to temporarily hide/unhide them (by adding overflow:hidden on their iframe html element and then removing that style), they don't come back. So, it seems each scrollbar is only present to allow the user to scroll the area that's covered up by the other scrollbar. :)

EXPECTED RESULTS: No unnecessary scrollbars.

Chrome gives EXPECTED RESULTS, (and as noted above, I can jostle Firefox into giving expected results by a tweak in devtools; but initially they're present).

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: screenshot of expected rendering, from Chrome (no scrollbars)

Comment 2

[Daniel Holbert [:dholbert]]

Two things that are worth noting:
(1) Sponsored posts do have a more direct link to "why did I see this ad", as a menu option on the post itself. But I don't hit this bug when I use this option. I've only hit the bug when using the "hide ad" and then clicking through to "why" from that ad-hiding UI, using the process described in the STR.

(2) Sometimes I can scroll for quite a while without seeing any sponsored posts at all (even without any adblocker) -- and obviously, if you can't find a sponsored post, then this bug is impossible to test. So, be warned about that. :) (I'm not 100% sure, but based on my observations, I'm sort of guessing that Facebook might suppress sponsored posts in your newsfeed for some period of time after you've hidden an ad; this makes it difficult to reproduce this bug in two browsers side-by-side, obviously.)

Comment 3

[Daniel Holbert [:dholbert]]

I suspect this bug has to do with the fact that this piece of content assembled dynamically, and Facebook probably throws some content off out of the scrollable area at first (prompting us to create scrollbars), and then they either resize the area or remove the overflowing content such that the scrollbars technically aren't necessary anymore, but we can't tell because we don't opportunistically try to remove scrollbars once we're showing them, as long as there's still room to scroll (which there is, when both scrollbars are showing).

Comment 4

[Mats Palmgren (inactive)]

Fwiw, we a few similar older bugs if you search for "unnecessary scrollbar", e.g. bug 442682.