Browser plugins can add functionality to the game right in your browser where the games is. Please find some useful examples below and also check the info in this link https://studio88.ba/review/in-depth-review-of-wild-card-city-casino/:
One of the advantages of Firefox is that add-ons can be created quit easily. Due to this, a lot of add-ons ARE beging created. One of the add-ons I use for Hattrick is PsicoTSI.
Foxtrick is a browser extension for hattrick. It enables the usage of skins in hattrick. Foxtrick makes calculations and creates extra shortcuts within Hattrick. In short: it makes external Hattrick Tools available right into the user interface of hattrick.