Although Firefox lists a great many translate add-ons, none of those I've looked at is compatible with the add-ons I've already installed (primarily one particular add-on that I find very useful). So I was pleased that a Google search came up with translate4.eu, which I very likely could use and which invites me to download it for Firefox. However Mozilla blocks its installation unless I "allow" it. I note also that this program is missing from Firefox's very extensive list of available add-ons. What danger is there if I allow this installation?