Group change on unloaded tab are not saved, and users are not warned by that behaviour

[PikachuEXE]

tabkit/tab-highlighter#3

Why the behaviour exsits

This is due to how session store works in Firefox
If a tab is unloaded, setting attributes on it won't be remembered
So if you have some load tabs & unloaded tabs and you try to change the group (or ungroup),
the result for loaded tabs will be remembered, while those for unload tabs will be discarded (after restart)

Solution

User should be warned to take action to load all affected tabs