While the default implementation of Seamonkey for LXLE is enabled with numerous addons the memory usage of each was checked before approval. All extensions run really low to almost no frontend footprint whatsoever given their task. The following extension is used to calculate memory usage of the included addons.

This extension may prove useful to users as well who have added their own addons/extensions and would like to know how it's affecting the browser in terms of weight and in turn performance.

https://addons.mozilla.org/en-US/seamonkey/addon/about-addons-memory-2016/

Click 'add to SeaMonkey' and 'install anyway'.

It's pretty easy to use. Hope it helps and clears some 'wonder' up.