(Probably a lot easier if Epiphany is fixed to place some X- Category to its desktop files, and then matching is done using standard GMenu tools) (Probably still easier if you use ShellAppSystem and match on the ShellApp:id) In any case, when disabling the extension, you need to cancel the file monitor and remove the deferred work you create at line 208.

Ok I made it cancel the monitor in the destroy method, thanks. About deferred works, as far as I know there's no way to remove them. So, since I guess they aren't so necessary for my extension, I just removed them. About the ShellAppSystem, I wrote this extension so that it can find webapps even when they aren't linked into {userdatadir}/applications, because epiphany still considers them present even in that case. It can also turn useful if you have more profiles listing the same apps, because in that case softlinks get removed and remade to the last profile.