Vertical tabs have an animation issue which hides the last tab in the list when there are enough open to scroll

[sluchianov]

Firefox v141.0

When the vertical tabs list overflows and has a scroll bar, the animation of it opening and closing causes the very last tab in the list to scroll out of view.

What's happening is that the >> icon at the bottom of the list turns into the expanded options on hover (settings, bookmarks, history, etc), but when the sidebar is no longer hovered, those settings are NOT replaced again with the >> icon when the sidebar begins to collapse. Instead, the animation has the new tab (+) icon as the very bottom icon in the sidebar. As soon as the animation finishes, the >> icon spawns in and shifts the entire contents of the sidebar upwards. This results in the very bottom tab in the list being covered up by the new tab (+) icon.

This is generally not an issue when you are going to select any tab in the sidebar except for the last one. However this IS an issue when you DO want to click on the last tab in the list as it ends up being covered by the new tab (+) icon every single time you hover the sidebar. This results in needing to scroll down one line to access that last tab every single time you hover the list.

[Spidersonic]

Firefox v141.0

I have that same issue on a computer which is running in 4K. On my laptop, which runs in 1080p, this issue doesn't occur. Maybe it only happens in specific resolutions?

[sluchianov]

Oh interesting! My screen is 2560x1440 so there's another data point. I unfortunately don't have a true 1080p screen to verify with, but I'll test out some different resolution at the OS level.

[Spidersonic]

Let me know about your findings 🙂

As for me, my main computer is at 3840x2160 with a recommended scaling of 300% and my laptop is at 1920x1080 with a recommended scaling of 125%. This issue occurs on the first configuration but not on the other one.

[sluchianov]

I tried a bunch of resolutions from 1080p up to 4k on my laptop, tested it on my Samsung G9 with 3840x1080 and 5120x1440, and tried scaling from 100% to 300% on each resolution. Everything had the animation issue.

[Spidersonic]

This issue might not be related to the resolution then. I'll try and compare the about:config pages on both of my instances when I have the time but it might take a while. I'll let you know if I find anything 🙂

[Spidersonic]

@sluchianov 

I found something: In "about:config", there's a setting called "sidebar.animation.enabled". By default, it's on "true". If I set it to "false", the issue disappears.

Funny thing is, this smooth animation plays out on my main rig (the 4K one), where it seems to be triggering the issue when the sidebar shrinks. On my laptop (the 1080p one), the sidebar acts as if this setting is disabled despite it being enabled in "about:config". If I turn it off and then turn it back on, my laptop becomes unable to expand the sidebar at all when I hover over it.

[sluchianov]

I can confirm that disabling that setting fixes the scrolling bug! Looks like I'll be keeping the animations off 😄

[Spidersonic]

I'm glad it worked for you too. I've disabled the sidebar animations on both of my computers and have been enjoying seeing the sidebar function flawlessly ever since 😎