Unfortunately all browsers require you to save the file locally so it can actually run. Even IE saves the file in a folder on the OS drive. If you just save the file in the default location, you can locate it by right-clicking the file and choosing Open Containing Folder. Then you can delete the file after you've finished using it. Sorry about the delay with the support.

That's not a "problem", that's the way Firefox is intended to work. But Add-ons exist to modify Firefox in many ways.

OpenDownload²
https://addons.mozilla.org/en-US/firefox/addon/opendownload-10902/

Thank you. I realise Firefox people are volunteers. But IE can open an attached file immediately, one click, allowing me to work on it then save it where I want (defaulting to the previous save location). Firefox used to do this too. Now, after an upgrade, it doesn't. I don't want a laborious 5-layer saving, then another separate 5-layer finding & opening process just to OPEN/VIEW an emailed Word or Excel file before editing it. I'm a lecturer receiving multiple files for review continually. IE opens a file immediately to allow editing, remembers where you saved the last file and takes you there to save it. Doing the same action via Firefox now is a recipe for RSI. Several other users have noted this but there seems no solution was offered.

After the OpenDownload2 add-on, no change. There is no "Open File" dialogue when clicking Open for an attached file in Firefox (and so no "Run" or other options), just the same Save As dialogue box as before, requiring a laborious saving process to a remote folder, then a laborious re-locating-the-file process before it can be opened.