OK, thanks for the information. SeaMonkey still does not support WebExtensions, and as far as I know there are no immediate plans for SeaMonkey to adopt it, which is why I have been using the Greasemonkey Port. I don't know much about Electrolysis (e10s) and to what extent it's supported in the current version of SeaMonkey; there seems to be precious little discussion of this matter in the SeaMonkey minutes and the SeaMonkey Bugzilla. It could be that it is already supported (since the latest SeaMonkey shares the same backend as Firefox 60.6 from last year) but that nobody bothered to announce this. If e10s is the only technical issue holding back further development of the port, then I can try to find out whether and to what extent SeaMonkey supports e10s and if there are any plans regarding it.

Are there any plans to update the GreaseMonkey port for Seamonkey, which I understand is developed by one of the admins here, Marti Martz? The latest release of the port is for GreaseMonkey 3.10.0.1rc3, which is about four years old, whereas the latest release of GreaseMonkey proper is 4.10. I suspect that the modern user scripts that I'm running may not be functioning very well due to running on a very old version of GreaseMonkey.

If there are no plans by the original developer to continue maintaining the port, perhaps he might provide or point to some documentation on what's involved in preparing the ports? If it's not too much work, and doesn't require too many skills that I don't already have, then maybe I could help out.