Affected versions

• 77.0.1
• 78.0b7
• 79.0a1 (2020-06-14)

Affected platforms

• Windows
• Ubuntu
• macOS

Steps to reproduce

1. Open any page (eg. https://www.catster.com/wp-content/uploads/2017/08/A-fluffy-cat-looking-funny-surprised-or-concerned.jpg)
2. Zoom in using CTRL + wheel mouse till 270% scale
3. Open the Hamburger Menu
4. Click on the Zoom in (+) button

Expected result

• The button is functional, the zoom level changes to 300%

Actual result

• The button has the implicit effects on interaction, but triggers no action

Regression range

• Reproducible on 76.0a1, I will provide a more accurate regression asap.

Additional notes

• No error is shown inside the browser console

https://searchfox.org/mozilla-central/rev/25d491b7924493b5d4bedc07841a1cd92f271100/toolkit/content/viewZoomOverlay.js#86-91 will probably snap the 270% zoom to 300% and then refuse to find a higher index. I'm not sure if this is intentional - if not, then the bug is either in the toolkit viewZoomOverlay.js code or in the browser-fullZoom.js code that invokes it. Moving bug to toolkit to start.

I've restrained the regression range only to the following (due to some broken builds in between): https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=82ae3b4e2215&tochange=0f1d42a6745a

The severity field is not set for this bug.
:Dolske, could you have a look please?

For more information, please visit auto_nag documentation.

This should be fixed by bug 1655223 when we make mouse scroll-based zoom consistent with keyboard/menu-based zoom.