Warn users about the impact of having too many filters installed
In the legacy version of Adblock Plus for Firefox we had a warning for when you added multiple filter lists to inform you about the negative performance and memory impact of having lots of filters.
With the transition to web extensions on Firefox we also introduced a new mobile options page which is meant to be replaced with a responsive version of the desktop options page. Unlike its predecessor, that page allows the user to add multiple filter lists. Therefore we should work on ways to at least inform users so that they can avoid excessive memory usage and other issues that could potentially be caused by having too many filters.
Any thresholds we set should probably be lower on mobile devices than on desktop ones.