It's a one time fee.
I just tested to see if Firefox 47 could load my extension, and it silently fails (Firefox now has partial support for what Mozilla calls WebExtensions, which is basically Chrome/Chromium extensions).
I'm now going to test whether the Chrome extension works in Opera. I expect to have better luck.
EDIT: I just tested the extension in the latest Opera. It works perfectly
I'm just going to rename it so that it becomes "Clouttery for Opera".
I just tested to see if Firefox 47 could load my extension, and it silently fails (Firefox now has partial support for what Mozilla calls WebExtensions, which is basically Chrome/Chromium extensions).
I'm now going to test whether the Chrome extension works in Opera. I expect to have better luck.
EDIT: I just tested the extension in the latest Opera. It works perfectly
I'm just going to rename it so that it becomes "Clouttery for Opera".