Firefox honors the content-type header sent by the server. IE sniffs the beginning of the download to see whether the server is telling the truth. That's why you see some differences and why the solution is to add a new file type on the server.

In the short run, is it the type of link you can right-click and Save Link As?

If not, hmmm, workarounds. I think there used to be an add-on which could use file extensions to change how files are handled, but I couldn't find it in a quick search.

Use "Save Link as" in the right-click context menu or hold down the Alt key and left-click the link to get the save file dialog.

You need to set the browser.altClickSave to true on the about:config page to make the latter work.

• http://kb.mozillazine.org/about:config

I changed the setting in the about config and will see if it help as the link I'm trying to download are not from a web site, they come directly to me so I can't even alt click but I will try to see if it help pressing alt when I press the enter key.

I will keep you updated on the result on the next link I receive.

Changing the setting for alt click didn't help, I press alt after pasting the link and then press enter, open the file in a new tab but still as plain text. I also tried pressing alt 1 sec after pressing enter but the file still appear as text instead of archive.

If the server is not configured to send 7z files as a download, then we are a little bit stuck. To create a right-clickable link from a URL you've copied, you could use a bookmarklet.

A bookmarklet is a script that you save as a bookmark, for convenience, you can save it to the Bookmarks Toolbar. This one creates a new window/tab with the link.

(1) Copy the following line of code (it's all one long line):

javascript:var u=prompt("Paste URL");if(u.length>0){var w=window.open("about:blank","_blank");w.document.write('<p><a href="'+u+'">Right-click and Save Link As</a></p>');w.document.close();} void 0;

(2) Right-click the Bookmarks Toolbar and choose New Bookmark

(3) Paste the code in as the Location

(4) Name the bookmark as you wish (for example, Link-it)

To create the link, click the button and paste the URL.

Hopefully someone will come up with a better workaround. And meanwhile, please complain to the site if they are a repeat offender. Very specifically, they need to do something like this in their server configuration files:

AddType application/x-7z-compressed .7z