The Private Browsing icon alone is helpful enough to identify a Private Window. Including the writing in the Tabs bar is redundant while also reducing space to display tabs.

While I think that there may be some merit to a Dark-themed Private Browsing Mode, it should be a separate switch in about:preferences. The current implementation prevents the "Follow System" theme to serve its purpose: if my OS has Dark Mode enabled then all apps should have it enabled as well, but if my OS is in Light Mode, everything would be in Light Mode EXCEPT Private Windows. I'd rather let the "Follow System" setting to serve its original purpose.

I also tend to agree that separating Private Windows and Standard Windows into two Taskbar icons is a little counterintuitive in maintaining ou privacy. Furthermore I personnally prefer to have all my Windows, Private or otherwise, stacked behind the same Taskbar Icon, since I can check at a glance in the Window's preview if I am in a Private window with the Icon in the Tabs bar. Perhaps there are different user cases, but I use both Private and Standard Windows at the same time, and it is neither hard nore time consuming to check in the Window's preview what Tabs are there and wether they are private or not based on the Tabs (such as the websites opened or the general "theme" of my opened tabs). In the end I'd think that it would also be easier to switch between Standard and Private Tabs, without having to face a longer distance between the two Taskbar Icons.

While my next comment isn't specifically related just to the changes in Private Browsing, I would like to express my appreciation that this discussion was launched by the Firefox Team. It helps remind us all that there truly is a link between Firefox developpers and its users, and it shows some openness toward feedback, something reinforced by the proactive launch of this thread. This is much more tactful and respectful than other previous changes where we were just placed before an accomplished fact (looking at you, "optimised" download flow).

If Firefox would commit to continue hosting such feedbacks (perhaps while the changes are still in Beta, before landing in Stable versions), we might not always agree on the necessity or usefulness of such changes, but on the other hand it might help us Users regain some trust and respect in our Browser.