Enqueue visited WEB pages for storage and indexing by Recoll. Needs Recoll version 1.23.5 or later onLinux, Recoll 1.26.2 on Windows or Mac. Important:

Set the webdownloadsdir variable to the location of your default downloads directory in your recoll.conf Recoll configuration file (only needed if the location differs from the default $HOME/Downloads).
The downloads dialog will appear the first time a page is saved. Click the Save file and Do this automatically for files like this from now on checkboxes so that things happen automatically in the future (the saved data has a specific MIME type, so this will only affect this addon).
Since version 98.0, Firefox automatically opens the download dropdown list when a download completes, so it happens all the time when the Recoll WE extension is active; A workaround a kind user found is to set browser.download.alwaysOpenPanel to false (source: https://www.reddit.com/r/firefox/comments/tb56js/firefox_opens_download_dropdown_automatically/)

Also see the extension documentation page (mainly about preferences options). Many thanks to the Save Page WE add-on, from which a lot of code and ideas were 'borrowed'.