[Technical Note] It seems sometimes the extension simply just not discard a background tab that it should. Why?

Skipping the discarding has two main reasons: 1. a tab matches a condition that prevents discarding (e.g. do not discard this tab is checked for this particular tab from the popup window). From version 0.3.2, the extension adds a tooltip text to the toolbar button for this particular tab if such a condition meets. 2. The number of not-discarded tabs is less than the number that the user sets on the options page. Still, the extension might sometimes not discard tabs with no good reason. That is true in fact. To be optimal, this extension only requests checking the discarding conditions when it really is necessary. To be more precise, a tab will request the check only once when it just moved to background after the user-defined discarding period is over. That's it. So a single background tab cannot ask for discarding more than once. There are some rare situations where a tab does the request and it gets rejected for one of the above reasons. In this case, this tab is not going to be discarded unless at least more than one tab gets opened. To generate this bug you can set discarding period to 10 and the maximum number of tabs to 1. Now open a tab and browse a website. Open the second tab and wait for 10 seconds then load a second website. You are expecting the first tab to be discarded but since its discarding request is sent before there are two real tabs, this request is being ignored. The only way to discard the first tab now is to switch to another tab so that the second tab this time sends a new discarding request which results in the first tab to be discarded.