Trying to reproduce this, I can see the tabs tray not opening fully in vertical mode with no or few tabs open, but it does always open fully in horizontal mode on my phone. It seems on your devices, Firefox does not identify the orientation mode correctly for this.

So, can't reproduce on Samsung J4+ Android 9. Maybe others can reproduce on other devices.

Trying to reproduce this, I can see the tabs tray not opening fully in vertical mode with no or few tabs open, but it does always open fully in horizontal mode on my phone. It seems on your devices, Firefox does not identify the orientation mode correctly for this. So, can't reproduce on Samsung J4+ Android 9. Maybe others can reproduce on other devices.

Vertical mode is fine on my end. It's horizontal when things don't behave as expected. It's strange because I have 2 phones that have the same behavior. It's as if there's a setting I have enabled/disabled which impacts this behavior.

Are your settings synchronized? Both your devices have Adreno GPUs, but different ones (also differing from mine). Can you access about:config? Maybe setting gfx.webrender.software to true makes a difference. (Wild guess.)

Are your settings synchronized? Both your devices have Adreno GPUs, but different ones (also differing from mine). Can you access about:config? Maybe setting gfx.webrender.software to true makes a difference. (Wild guess.)

Are your settings synchronized? Both your devices have Adreno GPUs, but different ones (also differing from mine). Can you access about:config? Maybe setting gfx.webrender.software to true makes a difference. (Wild guess.)

I have sync set up with my Desktop and both phones. I toggled 'gfx.webrender.software' to 'true', but no change in behavior unfortunately.

Are your settings synchronized? Both your devices have Adreno GPUs, but different ones (also differing from mine). Can you access about:config? Maybe setting gfx.webrender.software to true makes a difference. (Wild guess.)

I have sync set up on both phones and a desktop under the same account. However, I have the same behavior with a fresh install without sync / unmodified settings.

I toggled 'gfx.webrender.software' to 'true', but no change in behavior unfortunately.

Some more info on behavior.

If I open the tab list vertically and then rotate to horizontal mode, the tab list will display properly. But closing, and then reopening still results in the tab list not opening fully.

So it's probably not graphics hardware, as the config switch didn't make a difference. Or wait - did you stop and restart the app? I had to to see another problem solved by the switch. I suspected the display ratio might have confused the tray position calculation, but it's different for your devices.

So it's probably not graphics hardware, as the config switch didn't make a difference. Or wait - did you stop and restart the app? I had to to see another problem solved by the switch. I suspected the display ratio might have confused the tray position calculation, but it's different for your devices.

Yes, I restarted the app after the change.

I did some experimenting and found that I need 4 tabs open for the tab tray to open completely. I uploaded images of what the tab tray looks like with 4 vs 3 tabs open after clicking the tab tray button.

Something else I observed: If I start Firefox already in horizontal mode, then the tab tray opens fully consistently.

This is a workaround I'm willing to live with as I can't tell what's causing this issue.