Just a matter of convenience... I believe on a large screen it makes more sense to have fresher tabs closer to the top, the most active area of the browser (all the controls are there), as less eye movement between them is required.
FWIW, I have a human factors degree and was lucky enough to work on a very popular browser for a number of years. I can say with very high confidence that the new tab button should be at the top of the tab strip (more info in the Edge forum link)
This is a great idea! I get that Firefox is too small to make risky decisions and its UI just copies the popular solutions, but the current design is just backward. The newest tabs are the furthest to the bottom, so despite being the most likely to be interacted with they are miles from the rest of the UI. They should be right at the top to stay in a convenient range from the address bar and the rest of the buttons. It's the same with the "new tab" button, it's all the way down and it keeps moving around as you're opening and closing tabs. It should be right at the top, not moving and close to the address bar that is the next thing you're working with after creating a new tab. The current design seems to be disregarding the basic usability principles for no apparent reason and I find it baffling. Having the default identical to other browsers makes sense, but there needs to be a possibility to make the UI actually good.
I completely agree, it only make sense to move all of the controls to the top of the screen, as it's less movement of the cursor around the screen, hence time saved. With current implementation I have to constantly move the cursor to the bottom, which has no other controls but sidebar's.
Devs should implement an option to move the sidebar controls position to the top of the screen and make new tabs appear at the top. I understand that it may introduce discrepancy with other menus that list tabs, such as "List all tabs" menu or "Recent browsing" menu, which should, in my opinion, be left sorted where new tabs appear at the bottom. Also, the Ctrl + PgUp/PgDown hotkeys function would need to be reversed so that Ctrl + PgDown would move you to the older (left, if viewed on a regular tab bar) tab. So yeah, the implementation is not as simple as it seems at first. But the better UX of controls being concentrated in one place outweighs this potential confusion, in my opinion.
I'm using the new vertical tabs feature and I do like it! Thus, I want to give feedback in order to best help it along.
The problem:
With a lot of tabs open, the "new tab" button approaches the bottom of the screen. In this case, it can be annoying to move the cursor from the "new tab" button all the way up to the bookmark bar, then back down to access the content of the webpage or switch to another tab.
I am familiar with shortcuts like ctrl+t and use them often, but sometimes I'd rather operate my computer with just a mouse. (Plus, not everyone knows or uses shortcuts!)
The solution:
Move the new tab button to the top of the list of tabs. This has the added benefits of clustering most-used buttons at the top left corner for ease of use. It would also fix the "new tab" button in place, helping muscle memory.
This would ideally be a toggle in settings, so users can try out and select which layout they prefer.