Is there a way to save the currently opened tabs (URLs) of Firefox into a text file?
Use the URL Lister add-on.
Shows the URLs of all the tabs in a textarea so that it can be copied easily.
I think Multiple Tab Handler can do this for you.
There is this module, which can format (a bit) the list if you want : https://addons.mozilla.org/fr/firefox/addon/send-tab-urls/ It saved my day, thanks to its developer !