I replied PM, this is a copy with an screenshot
The problem is probably caused by mis-communication between firefox and OSX, when you drag the file from desktop into firefox, firefox only writes down the address of the file, rather than the content.
Here is several suggestion, either one should help your problem.
1. after translation, selected the translated text in sherlock, instead of dragging it to desktop, you can drag it directly into mail-composing area of yahoo mail within firefox window (I will post to your original thread in the forum, with an attachment showing the dragging process.).
2. or if dragging is not very easy (I found it hard to drag text from sherlock. You can select the texted, press keyboard combo "cmd(apple key)+c" to copy the text, then goto yahoo mail's composing area in firefox, press key combo "cmd+v", it should be pasted directly.
3. find some other online translating service, such as
google language tool
let me know if you have further problem.
Good luck