There have been reports from some users that Clippings no longer functions after the upgrade to version 5.5.
However, these reports are being posted to the Clippings page on the Mozilla Add-ons site, with missing details on OS, Firefox or Thunderbird version, and any error messages observed.
Without these important details, I'm unable to troubleshoot to determine the cause, and ultimately find a fix for these reported problems.
If you are encountering problems after upgrading to Clippings 5.5, please post to the AE Creations Help and Support forums. Please indicate which version of Firefox or Thunderbird you are using, as well as your operating system and its version. If there were any error messages that appeared, please provide the error message contents as well. (If none were visible, open the Browser Console by pressing CTRL+SHIFT+J or Command+Shift+J, and copy/paste any messages that may appear.)
UPDATE (2017-10-14): The cause of the issue has been identified and fixed. A new minor release of Clippings will be available soon. For now, Clippings 5.5 is unavailable.