Sorry, they probably detect hotlinking (i.e. direct downloading) specifically to stop addons like this. Thank you for giving a reasonable rating to a functioning product, unlike all the petulant reviewers that go straight to 1 star for the silliest reasons as if it's a completely defective piece of junk.

Filenames and extensions depend entirely on the hosting server. Renaming using a.o. the page title is implemented but not supported by firefox itself. Thank you for the reasonable rating, all things considered, unlike the way some people rate projects.

Certainly a fair remark, though just for clarity I'd like to point out this is simply the nature of twitter's image hosting/linking, not a shortcoming in the addon. File extensions are a mere semantic convention and mostly only relevant in filesystems for human users. In HTTP-hosted resources, they're a mere courtesy a server/URL can decide not to offer. Other websites will similarly not include a file extension, and there's little an addon or browser can do about it (especially in firefox, which still doesn't implement filename manipulation for addons).

I just checked again, and the file extension could be derived from other data in twitter's URLs, but it would require both the missing renaming implementation in firefox as well as special handling code in my addon just for twitter. The latter I indeed choose not to implement, even for the chrome-based browsers that would support it. :)

That's not a bad idea, though the exact format will be an issue, and you could achieve this through your file manager and a renaming program, but that's understandably more effort. Maybe I can add y/m/d h/m/s variables that you can use as desired. I'm slogging through technical work on my addons right now and don't expect to work on new features for some time still though. Please follow progress or discuss here: https://gitlab.com/Marnes/doubleclick-image-downloader/-/issues/78

Modern addons are not able to control download locations, sorry. This is a deliberate design regarding user settings in browsers. I couldn't implement it even if I wanted to.

Thanks for the detailed feedback. As for file extensions, extensions are not actually a required thing in filenames, they're more of a loose convention. Websites tend to forego them depending on how their images are loaded (e.g. from data streams rather than files). It's the browser's responsibility to determine an extension if at all possible, based on data from the webserver if provided (such as a suggested filename, with or without extension). It's really not within an addon's power to ensure the presence of file extensions, or infer any, sorry.

Only via your browser settings. Addons are not allowed to manipulate download locations.

Notifications are controlled by firefox, addons can't change their timing, sorry. If the notifications bother you, you can turn them off.

Glad you like it. Choosing a custom downloads folder will not be done: it's a bad idea and not even possible in/allowed by any browser anyway. All downloads in a browser will always go to the browser's download folder (or a subfolder within it).