Tecknity extension

Good day.
Please help i’m new to firefox, i’m trying to install " Tecknity extension " but keep getting "oops error " https://addons.mozilla.org/en-US/firefox/addon/accounts-pool/

and like Google chrome does firefox have a developer tools?
Thanx in advance

Where did you get the link to that extension from? It seems like it’s not currently publicly available. Your best bet to find out why is to contact its developer.

Yes, there are developer tools. You can find them in the “Web Developer” menu. Documentation is on MDN iirc.