Google Images recently updated, and the previous technique to find the original images past 100 (the preloaded amount) doesn't work anymore. I've implemented a fix for the userscript version, but unfortunately getting this to work on the extension version is a bit trickier, and might not land in the next release (it needs to intercept HTTP calls, which is definitely my least favorite approach towards supporting a website).
I've tracked the feature here: https://github.com/qsniyg/maxurl/issues/1533 . Note that once it's implemented, you will need to enable "Rules intercepting HTTP requests" (under the Rules tab). It's disabled by default because it carries a fingerprinting risk.

Can you try with the latest version (2023.8.0)? I believe I fixed most of the DeviantArt issues there :)
Edit: Glad to know it works for you again!

Sorry for the late reply. The next version will fix Instagram (and support 1440x for posts without needing the mobile API). Tumblr will also be fixed. You can side-load the Github version in the meantime if you wish, they should work properly there :)

Indeed. I've submitted it, but they haven't yet approved it... soon I hope!

Edit: It's up now!

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! :)