UPDATE:
A new version 2.8.0 of xIFr has been released. It will try to re-define menu-item at every new startup of the browser. I haven't tried deleting webext.sc.lz4 myself. Not convinced that it is a good idea to do so. But my best guess is, that this will make menu-item come back for you at first browser-restart after extension has updated (if you haven't already fixed menu-item by un/re-installing of xIFr).

/Stig



OLD REPLY:
You seem very confident ii is a problem with xIFr. Do you have some technical insight and are able to elaborate? I'm just using the recommended way from documentation to define menu item. That is using browser.menus.create() in browser.runtime.onInstalled handler.

I find it hard to blame xIFr, if you delete a file in Firefox profile using CCleaner. What CCleaner does is sometimes wrong/bad. But there's a Firefox bug that eventually could be related though: https://bugzilla.mozilla.org/show_bug.cgi?id=1817287 ? (Though I had the impression that bug was related to MV3 extensions only - xIFr is still only an MV2 extension).

For now, I will assume you can get the menu-item back by un-installing and re-installing xIFr? But I will do some investigation and see if I can make menu-item more robust or "self-regenerating". I hope you can test/verify if a future xIFr-version eventually fixes the problem?