With the update to Mediawiki this week, the ability for the additions of groups and maybe buttons has been reported at English Wikisource https://en.wikisource.org/wiki/Wikisource:Administrators%27_noticeboard#Special:Gadgets
For those using the Wikieditor toolbar it has now disabled all the extension's specific editing tools https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FProofreadPage/HEAD/modules%2Fpage%2Fext.proofreadpage.page.edit.js thus making editing impossible in certain aspects.
Assistance is requested.
See https://en.wikisource.org/wiki/Wikisource:Administrators%27_noticeboard#Resource_Loader_issue_needs_outside_guidance