The link you posted (replacing xxx) works on my end, but my guess is that it's some kind of regional update or layout change of some kind that causes it to fail for you... Can you contact me through one of the links at the bottom of https://addons.mozilla.org/en-US/firefox/addon/image-max-url/ ? (Unfortunately it's not possible to have a back and forth with firefox reviews)

Hopefully we can fix this :)

Sorry, I'm not sure I understand. I've tried it on the image below the Главное tab, and it works for me. If this is not the image you're referring to, can you send a screenshot of where the image is on yandex.ru?
If this is the image you're referring to though, can you send me your settings? (Export button at the top of the options page) Hopefully that will let me reproduce your problem and find a fix :)
My contact information is listed at the bottom of the addon's page.
Edit: Sorry, I hadn't seen your edit. My email(+pgp key) is listed here: https://qsniyg.github.io/

I can't actually seem to replicate the issue, sorry! I tried under Waterfox Classic 2021.02 as you mentioned, and it appears to work fine for me. Would you mind sending your settings (through the options->export button)? Contact links are available on the extension page (use whatever you're more comfortable with). Also, could you send an example link that doesn't work for you? For me, https://pbs.twimg.com/media/DlOC3mOWsAEi1ld.jpg redirects properly to https://pbs.twimg.com/media/DlOC3mOWsAEi1ld?format=jpg&name=orig .
It could be that there's a specific combination of settings that causes it to break, it wouldn't be the first time that has happened under Waterfox (due to its older JS engine).

Which websites did you try it on? For a lot of sites, it won't be able to find a larger version, because it's the largest version that the site hosts. It doesn't perform a reverse image search, it complements using one, as often reverse image search engines don't link to the largest version a website hosts (as they have no knowledge of how to do this). If, however, the site should does host a larger version and the script doesn't support it, please let me know!

Just to make sure it's not some bug however, can you check if https://pbs.twimg.com/media/DlOC3mOWsAEi1ld.jpg redirects to https://pbs.twimg.com/media/DlOC3mOWsAEi1ld.jpg?name=orig (or a similar URL)?

Hmm, according to another user it still appears to work, so it doesn't seem like the issue has to do with an Instagram update (thankfully!). Did you by any chance log out of instagram? It only works when you're logged in.

If not, can you contact me through one of the contact links in the addon's description? Matrix or discord would be ideal as it might require a bit of back and forth to find out what the issue is (but if not email/github/reddit is fine too). The reason I ask is that unfortunately there's no way to have a discussion over the firefox addons review page, so I can't really help troubleshoot the issue here.

Sorry you're having this issue, and hope we can get this fixed! :)

Sorry, there's currently no way to add manual rules. This is something I'd really like to add in the future (see https://github.com/qsniyg/maxurl/issues/41), but currently there are a few technical problems with implementing this for the moment (see the linked issue for a bit more detail on why).

If you want to request a new site to be added to the script, feel free to use any of the contact links listed at the bottom of the script's description, whichever you're most comfortable with. I'm more than happy to add any new website to the script, and if I'm online, I usually add them within minutes of being notified :)

If you'd rather add it to the script yourself (note that this will require sideloading the addon), I've written a bit of a guide here: https://github.com/qsniyg/maxurl/blob/master/CONTRIBUTING.md#websiterule-contributions. In your case, a rule like this should work: if (domain === "subdomain.your-website.com") return src.replace(/(\/[0-9]+-)small(\.[^/.]+)(?:[?#].*)?$/, "$1original$2");

By the way, while the github issue hasn't seen much activity for a while, this does not mean it's been forgotten or ignored, the script is already getting restructured in many areas, which will facilitate the implementation of this. It's just that it is pretty a massive project (currently requires rewriting >70,000 lines of source code - much of which will be automatically handled, but even that requires a very significant amount of work).

Glad to know it's helpful!!
I should note however that this does not replace using a reverse image search engine, but rather complements using one. It'll find larger versions stored within the website itself (either through URL patterns or API calls), which are sometimes larger than what reverse image search engines can find (unless they crawl a page that contains the original image), but if the original image uploaded on the site is smaller than what's available on another site (e.g. an image reuploaded to a blog), it won't be able find that version.