Sometimes it just started when I type messages on web.whatsapp.com (1-3 times per day), do something please, year ago same thing was happening. I mean when Addon is stopped! It just start refresh the page every 5 sec.

Excellent for notifying changes on multiple sites. Works on containers. It seems that the check boxes are not saved after it detects a change [when "Show notification (any changes)" is checked] in a tab and stops the timer. I had to use a macro just to automatically check them if they're unchecked. There should be a save options feature.

In the advanced option Random intervals, which start from 5 seconds are fixed. It will be better for users can edit and input their chosen second here.
Please add this option in your next update.
Thank You.