Signature attachment button in account settings no longer working; will not go to location of signature image on hard drive

I have had the same signature attachment for several years on my Thunderbird email, but for the last week, new messages and replies are no longer bringing in the signature image for my emails. Additionally, if I go into settings and try to choose the signature as a reset mechanism, the 'choose' button does not react at all....does not go to file selection window where I can reselect the signature again. I can create a v-card, but it is also not attaching. The attached image appears as if everthing is set-up correctly, but the feature is not functioning. Please advise.

Cheryl U.