For Angelfish, since it does not directly allow specifying custom rules, you have to create a local file with the rule:
echo '||forum.manjaro.org/assets/browser-detect-*.js' >
adblocklist.txt
then add the ruleset file to Angelfish under Settings / Adblock / (+):
Name: Local Blocklist
Url: file:///home/yourusername/adblocklist.txt