Zero compatible add-ons for Thinderbird 52.9.1 32 bits

I want to add signature addon to my Thunderbird but Firefox show the message that it can’t install the addon because it SEEMS to be corrupted.
There are 6 or about 20 addons concernig signature (including quite new ones) and NON OF THEM is OK according to Firefox!!!
What is going on??? Why can’t I install any addon??? :angry:
I have Firefox Quantum 61.0.1 (64 bits)

See this support post.