1578259 - [Windows] The last top site is wrongly displayed on a second row when horizontally resizing the browser to exactly 1134px

Status: NEW

(Firefox :: Top Sites, defect, P2)

Description

[Andreea Cupsa [:acupsa], Experiments QA]

Attachment: Top sites at 1134 px.png

[Affected versions]:

• Firefox Nightly 71.0a1, Build ID: 20190902094857
• Firefox Release Candidate 69, Build ID: 20190827005903

[Affected Platforms]:

• All Windows

[Steps to reproduce]:

1. Open the browser and open a new tab.
2. Horizontally resize the browser to 1135px.
3. Observe the top sites.

[Expected result]:

• The top sites are correctly displayed.

[Actual result]:

• The last top site is displayed on a second row.

[Regression window]:

• This issue is not reproducible on Firefox Release 68.0.2. Considering this, using mozregression tool I have found the following pushlog:
• Last good revision: ce21500c025e1435eb0dc2bdf168674d38a11b1f
• First bad revision: 07bb612a30b0c2f268a0ffcb50457315de37684e
• Pushlog:
  https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=ce21500c025e1435eb0dc2bdf168674d38a11b1f&tochange=07bb612a30b0c2f268a0ffcb50457315de37684e

[Notes]:

• This issue is not reproducible on Mac and Linux.
• Attached a screenshot of the issue.

Comment 1

[Andreea Cupsa [:acupsa], Experiments QA]

Ed, could you please take a look at this issue?

Comment 2

[Kate Hudson :k88hudson]

Redirecting to Scott

Comment 3

[Scott [:thecount] Downe]

I've tracked this down to the removal of fixed-to-top in https://github.com/mozilla/activity-stream/commit/570c5211dad31ac5d56893bc5affba7fd2c4528c which switched from block display of main to revert to flex

I'm guessing this is a combination of windows scrollbar size and flex vs block.

With windows, when this goes wrong, the outer-wrapper page width is 1105, with 32 px left and right padding, totals 1041px. When we set that elements child, we specify set its width to be 1042px. So with the fixed-to-top classname before the above patch, 1042px was enforced, because fixed-to-top made it block display. As soon as we removed fixed-to-top, it reverted to flex, which would constrain it to its available 1041px, which wasn't the expected space for topsites.

For linux and mac, the scrollbar is smaller (I suspect) and it has enough clearance, the main outer-wrapper is 1110px with 32 left and right padding, which totals 1046px which can comfortably fit the 1042px flex.

I'm guessing this isn't critical.