Rated 4 out of 5 stars
I really appreciate your effort in continuing the development of this great extension and it's great you have kept compatibility with SeaMonkey.
There's one feature I am missing from the original extension - in the Page Info window there was an additional tab with headers of the current page. This was very convenient if you wanted to quickly view the headers without opening Live HTTP Headers window and loading the page again.
Mozilla plans to drop support for all addons that aren't using the WebExtensions APIs, so this addon will die when that change comes.
I will try to keep the addon working until that point but I won't add any more features, because it's simply not worth to invest more time into this when it's gonna die soon anyway.
Everything, or almost everything this addon does can already be done with Firefox's built-in developer tools so there's really no necessity to re-create this addon as a WebExtension addon.