Comment 12 for bug 313439

It has been determined that mime types/file associations are causing this issue. The same mechanism that opens .html files (which are not executable) also executes .jar files as they are associated with java. In order to specify which type of file should be executed by a mime association would indeed fall under the category of feature request. keep in mind that with this same feature request would come the issue of some users not being able to load .html files or .pdf files or any other file association based upon permissions if implemented.

Suggestion: if .jar files are a major issue for you, then you might want to dis-associate them with java so you don't run into the issue of them executing them when you double click on them.

Marking as wishlist as a result as there is currently no mechanism in place to flag certain mime types as executable.