Updated reply to dev..... I am using a userscript now instead of your extension and it works perfectly, so I don't think it's a browser issue, nor an issue with ImgInn.

I have some alternate code you can try with your extension, but I can't post it into here as it won't let me do it, and I can't find another way to contact you.

Works Grate!
-As someone who doesn't have a Instagram account. The create account pop-up would block my ability to scroll. This fixed this issue for me.
-Currently on Firefox 145.0 (64-bit). Win10 Pro. Version 22H2.

Good

Very basic redirection. It works, but it will try to forward every IG address including subdomains to ImgInn even though ImgInn only mirrors user pages. It does not seem to allow setting exceptions (as necessary for private pages or those that took down the ImgInn page) or skipping the redirect on demand. If you need to return to the original site for any reason, you will have to disable the extension and then re-enable it after.

Edit for dev's information request: To my knowledge, ImgInn only has an interface for user content so all other subdomains (i.e. not www) would not be a valid redirect. An example of which is help.* for the site's help pages.