As I suspected, the pop-up is coming from your extension's developer, so it may mean that you're not up to date...either Safari, the extension, or both.
I've got no idea what Firefox may have done to "fix" the problem, but I can reasonably guess that it installed the correct or, as the case may be, appropriate version.
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
