I am using 6.15.2 and when I try to edit an .xlsx file I am prompted to download the Atlassian Companion. This is what I am doing on both Chrome and Firefox:
0. Click the edit button for the .xlsx file that I want to edit.
1. See the pop-up that tells me about the Atlassian Companion.
2. Download Atlassian Companion .exe and run it.
3. Launch the app via the desktop shortcut (as an administrator).
4. Watch the mouse pointer spin for about 5 seconds.
5. Go back to my attachments page in Confluence and click the 'edit' button for the .xlsx file I used to be able to edit before the invention of the Atlassian Companion.
6. See the pop-up that tells me about the Atlassian Companion.
7. Repeat this endless loop until I am frustrated with the Atlassian Companion (which isn't very long).