Hi there, I've got a strange issue where some firefox clients are opening (as opposed to saving) a Microsoft Word 97-03 file (.doc) as a 07+ file (.docx). If the Save option is used the file is saved with the expected (and correct) .doc extension and Word opens the file just fine. However if the Open option is used, the user\local\temp file created is appended the wrong extension (e.g MyFile.doc.docx) and the Word application then corectly throws an error stating the contents do not match the extension and closes. "Word cannot open the file because the file format does not match the file extension." How can firefox save the files with different extensions based on the Save or Open action? Surely the filename provided by the server is the same in both circumstances? Why is Firefox appending the incorrect .docx extension for this .doc file? I have checked the application settings and it just states .doc, Action: Open with Word, have tried to reset Firefox and still the same. This is on Firefox 54.0.1 x86, application is an internal HRM system and the download is a historic HR document. I have checked other browsers and other instances of this browser version seem to open it fine (4/7 Firefox 54.0.1 installations are affected) they use the same version of Word (2013). Does anyone have any thoughts how this second extension is getting appended for some people when choosing the Open download action? Considered that the MIME type might override the extension on the filename value sent by the page but dont know how to check this. Other users browsing the same page do not get the issue and an affected user can log in on an unaffected user's computer with their own login and are not affected still (as is true the other way round, the issue is specific to the Firefox installation it would seem). Thanks in advance for any thoughts or troubleshooting suggestions, xeodeuk