From examining your screenshots, I see you are in the middle tab. That middle tab has now moved to first spot in the tab order. and shrunk itself. What happens if you visit your email, leaving this forum open? Looking at screenshot #3 in my imagination, I assume tab #3 will shrink in first place and the forum will be second again. Would that put your new home page tab into 3rd?

If I were running i9n 4 tabs, back and forth fro #2 to #4 and back t #3 then #2, I would possibly lose sight of wheren that tab went....

When a tab is moved to 1st position, it shrinks. If a tab is already there and shrunk, the 1st tab stays shrunk, and the tab being moved also shrinks.. It will only unshrink from what I can tell, is if it either 1) get moved PAST an unshrunk tab, or, 2) moved to the end of of the tabs, past the create new tab "+". I have not had time to fully explore the oddities of this new behavior. I just want my old tab behavior back, where the size is more or less determined by how many tabs are there, and otherwise they don't change size.

Is Mozilla run by a bunch of optimists ? There is a "Solved the problem" button, but not a "No it didn't solve the problem" button.

The feature you are describing is pinning tabs. There should be a patch later that addresses this issue, you can view updates at https://bugzilla.mozilla.org/show_bug.cgi?id=1984420.