[least]

It's more likely it has to do with all the work they're doing to getting the WebExtension API to work with WebKit which is a main selling feature for the MacOS version - using firefox and chrome extensions in a webkit-powered browser.

[freehorse]

And esp for the iOS version, where there are not many options for using extensions in other browsers. The only browser there that can use UBO, afaik. In MacOS it is a bit too buggy for me for daily use, ymmv.