See if this helps: https://www.mozilla.org/en-US/firefox/98.0/releasenotes/ Firefox has a new optimized download flow . . . .

https://support.mozilla.org/en-US/kb/manage-downloads-preferences-using-downloads-menu Changes to how file downloads are handled in Firefox version 98

• Firefox no longer asks what to do for each file by default
• Downloads panel automatically opens
• Downloaded files are saved to disk
• Set a default app to open a file type
• "Always Open Similar Files" option from the Downloads panel
• Frequently asked questions

You can set this pref to false on the about:config page to prevent opening the download panel on each download.

• browser.download.alwaysOpenPanel = false

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

You can right-click a specific item in the Downloads panel and choose "Always Open Similar Files" to make it open automatically. You can change the "Save" action to "Always Ask".

• https://support.mozilla.org/en-US/kb/change-firefox-behavior-when-open-file

Thanks for your replies. The trouble is that in Settings/General/Applications the only Applications listed are AVIF, XML, PDF, SVG, and WebP Image. How do I add other applications to this list, to enable me to instruct Firefox how to handle these files?

You can read about that in the article I linked above. Firefox add an action to applications when you click "Always Open Similar Files" in the context menu of a downloaded file.

• https://support.mozilla.org/en-US/kb/change-firefox-behavior-when-open-file