The default behavior is to hide the download toolbar button and only show it in the toolbar when a download happens or there are contents in the download panel.

The new download start animation includes the icon in the first few frames, so it appears to flash in and them disappear quickly as it transitions to the progress circle.

In the initial download case, we should remove the icon from those first few frames.

I've filed bug 1709904 and bug 1709902 to follow up on the issues Gijs identified in review.

https://hg.mozilla.org/mozilla-central/rev/8a9f8d02f9f3

Request for Uplift from the PM team

Comment on attachment 9220243 [details]
Bug 1709172 - Add a washidden attribute on #downloads-button; adjust fill color in start animation based on state we are animating from. r?Gijs

Beta/Release Uplift Approval Request

• User impact if declined: Flickery download animation for the first download in every session
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: n/a
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Relatively small changes to JS, CSS and image assets, has baked on nightly for a decent while now, applies completely cleanly to beta branch.
• String changes made/needed: Nope

Comment on attachment 9220243 [details]
Bug 1709172 - Add a washidden attribute on #downloads-button; adjust fill color in start animation based on state we are animating from. r?Gijs

Approved for 89 beta 15, thanks.

https://hg.mozilla.org/releases/mozilla-beta/rev/289220b2f5a7