I've been very pleased with the features of this add-in, but it may have a major memory leak.
I've been using this add-in in conjunction with a script that scrapes and reloads hundreds of web pages every few minutes. I've been having memory issues with Firefox lately, so I started disabling add-ins one at a time after running it for about a week.
The moment I disabled this add-in, the process memory decreased by 18 GiB. The decrease all came from the "heap-unclassified" section of the add-ins process. This suggests that this extension (over the course of potentially millions of page loads) has somehow been allocating memory to the heap but not freeing it.
I currently have a single rule set up to modify a CORS header. Let me know if I can gather any additional information to help confirm and/or debug this issue.