I'd noticed these small issues:
1. In a clean Firefox profile (without TMP),
when there's only one 1 tab open, it doesn't have a close button (x):

On the other hand, with TMP installed,
even if there's only one tab 1 open, it has a close button:

2. If you try to fix the above issue
by going to TMP>Events>Tab closing
and enable the setting 'Prevent last tab from closing'
then, indeed the last tab doesn't have a x button anymore.
BUT, then the following issue occurs:
if you have, eg 3 tabs open
and you have the setting Options>Tabs>'Warn me when closing window with multiple tabs' enabled,
then, if you try to close the firefox window
you get a message "You're about to close
2 tabs" (instead of 3).
Therefore, I'd like to make this suggestion:
please make the setting "Prevent last tab from closing" enabled by default (=to be enabled in a fresh TMP install).
And also, there's the second issue, with the incorrect number of the closed tabs in the warning.
Thanks a lot.