Have you looked into Firefox Multi Account Containers? I use this extension to quickly switch between multiple tab groups, some of which do use SSO while using the same service (e.g. Outlook). Plus, you can easily create new tabs like Ctrl + Shift + (#1-9) to open a container of your choice among other shortcuts. I know it doesn’t meet all your criteria, but each tab group has its own colour and/or icon to make them distinct, while being in the same window

I’m using AnySoftKeyboard, which is open source and also has swipe controls

Try FitoTrack. I’ve been using it for awhile, measurements are very close to what Strava records. It does lack the social element though

Perhaps right click on the sidebar -> disable compact mode? I haven’t had any issues moving tabs between windows, but then again I keep the sidebar persistent