What happens when you click on it   ?

I can't click it because it is from a screenshot I took before I refreshed Firefox. That's why I wanted to know what it was. Tried Google image search - came up empty...

I don't recognize it and 'Google' was no help either. You don't see any suspicious looking extensions,  that you are sure you never installed,  do you   ? Well, it disappeared as mysteriously as it came,   -   I wouldn't worry about it. But thruth be told :   I would want to know what it was, too   ! Maybe somebody else will recognize it   .....

Thank you. I will wait and see if anyone else can offer an answer. It's just driving me crazy. I don't think it is anything nefarious, just want to know because I must have used it for something. If I get nowhere, I will do a system restore and click on it at that point! Thanks so much!

If you refreshed Firefox then you should have an "Old Firefox Data" folder on the desktop with that profile and in this folder your installed extensions, so you should be able to find the extension that added this toolbar button in the extensions folder. For more details you can look in the extensions.json file.

cor-el said

If you refreshed Firefox then you should have an "Old Firefox Data" folder on the desktop with that profile and in this folder your installed extensions, so you should be able to find the extension that added this toolbar button in the extensions folder. For more details you can look in the extensions.json file.

Found it!! Thank you everyone for all of your help! https://addons.mozilla.org/en-us/firefox/addon/google-translator/