You can make your own but it will need a prefix like "web+catgifs:" or "ext+catgifs:" depending on how the custom url is handled (redirect vs webextension), to

You can make your own but it will need a prefix like "web+catgifs:" or "ext+catgifs:" depending on how the custom url is handled (redirect vs webextension), to be able to use custom urls without the prefix, you need to be on the whitelist. Thats why that little patch is cool, it enables us to build add-ons without requiring a prefix for the custom procotols used by popular dex stuff.