>>213628196
You asked the question, but anyway I can understand that worry. In which case uBlock Origin is probably the best idea (it's very widely used - pic related)

If you add it to Firefox it gets rid of adverts from many websites. And if you want to filter the Belgian in /brit/ then you just have to add this to your uBlock Origin filters:

boards.4chan.org##:matches-path(/int) div.thread:has(div.opContainer span.subject:has-text(/brit/i)) div.postContainer:has(> div.post > div.postInfo > span.nameBlock > span.flag:is(.flag-be))

I don't think you'll get malware. uBlock Origin is open source and widely trusted.