Dear @IXOYE
vandal-1.1.0-fx.xpi is yet another Firefox-targeting Web Extension that will not install on Serpent, because it's a type of WE called an "id-less" one... I have in the past, over many occasions, explained ad nauseam the "why" and "how-to" install such WEs on Serpent...
https://msfn.org/board/search/?&q=id-less&search_and_or=or&sortby=relevancy
For a more technical analysis on the "why",
https://msfn.org/board/topic/177125-my-browser-builds-part-1/page/147/?tab=comments#comment-1164701
For a more "practical" read,
https://msfn.org/board/topic/177125-my-browser-builds-part-1/page/100/?tab=comments#comment-1159013
https://msfn.org/board/topic/180462-my-browser-builds-part-2/page/133/?tab=comments#comment-1189182
perhaps could be of help...
Bottom line is, you have to edit the extension's manifest.json file so as to add a gecko-id block; repackage and then it'll install in St52...
St52 != FxESR 52.9.0, especially with regards to WE APIs, so installing in St52 won't guarantee perfect functioning...
And, please, DO NOT follow the advice given by my friend @ArcticFoxie ; transplanting a Fx profile onto St52 (or, worse, to St55) is a sure recipe for profile corruption, often times beyond repair! People, for the millionth time since I've been a member of this community, FIREFOX 52.9.x and SERPENT 52.9.0 are two different applications that have diverged so much over time, that their profiles are NOT INTERCHANGEABLE anymore (without risk of data corruption); just don't do it! Always start with a fresh St52 profile and only transfer vital parts such as bookmarks and, where applicable, passwords... Re-install crucial extensions as needed...