Does anyone know how to change the limit so these X’s ONLY appear on the active tab, or on full size tabs?
It is SO often I quickly click a tab, just to find out that I hit the X, and then need to reopen the tab.
I have been looking and googling for a setting for this.
I can not really imagine any common scenario where I would like to point out a tab and close it, without selecting it first. Of course I can academically think one up, but I really find it much more a pain in the neck than a useful feature.

I think they are about to adjust this behaviour a bit. Here is a screenshot from Chromium 70.0.3506.0: imgur.com/fYMxMll
Note on top the 81px wide tab does not have the [x]. The 88px in the middle has it. So it’s somewhere between these values where the [x] is being disabled.
On your screenshot the 81px ones (middle) still have the [x].
It was just a coincidence I ended up with a 81px tab, I adjusted my window to be 1280px wide.
I calculated the width on mine between | | separators of inactive tabs. On yours I used where the tab design starts arching up, on the active tab as it was easier: imgur.com/lKocyEI
Ah that sounds nice, it REALLY annoys me.
Have you EVER needed to close a particular tab that was not currently active?
Sure I can think up a scenario of mistakenly clicking a link that opens a new tab, that I want to close, but it is so academical, that the annoyance of in daily use mistakenly closing a tab I try to select by far outweighs the ‘convenience’.
(At the very least they should make the limit an option IMHO)
…For version 68.0 it is about 64 to 68 pixels, note this where SOME got the x’es???

Only some have, never noticed that. Very weird. I know in older Firefox versions you could remove that [x] completely, which I used to do. I never close tabs by clicking on that [x], I always use the mousewheel click to close them. I find it more convenient than trying to aim on that tiny button. Instead now I close them by mistake, of course. Difficult to understand what bothered the developers leaving that option in place.
(I was trying to find the limit by resizing the browser window, and got the above. Note the the tab distance WITH the x’es is slightly higher than without)