Note

• The issue seems similar with bug 1406002, but the steps to reproduce are a little different and the window buttons disappearing are not mentioned in the old bug so I considered this to be a different issue.

Affected versions

• Fx 66.0.5
  Fx 67.0
  Fx 68.0a1

Affected platforms

• Windows 10 & 7 x64
  Ubuntu 18.04

Steps to reproduce

1. Add a lot of pinned tabs to the browser (my case 15+)
2. Restart Firefox however you see fit.
3. Adjust the width of the Firefox window to be atleast half a screen or smaller.

Expected result

• The navigation buttons and the window buttons remain visible while adjusting the width.

Actual result

• The navigation buttons and the window buttons do not retain their position when adjusting width.

Regression range
*Will provide a regression range as soon as possible.

Additional notes

• The issue seems similar with bug 1406002, but the steps to reproduce are a little different and the window buttons disappearing are not mentioned in the old bug so I considered this to be a different issue.

Regression range:

• First bad:2018-11-06
• Last good:2018-11-05
• Pushlog: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=c41c4eba7e027bb7cc0735f94be19a8111790dc1&tochange=8d762aaeb5711d23e20b809fb8ec07cd04879bb2
• Potentially regressed by: Bug 1356920 - Hide the titlebar-buttonbox-container when in fullscreen mode. r=dao

I was about to file a duplicate of this because on a small window I lose the window controls due to this.

I guess potential solutions for this could include:

• Making pinned tabs independently scrollable (but what's the threshold to scroll pinned vs. unpinned tabs?).
• Somehow collapse them into a dropdown or something if they cause other stuff to overflow.
• Maybe something else?

I don't know if we have telemetry on how many pinned tabs are commonly used?