Stuken,
Although we don’t support third party plug-ins (normally, you’d have to go to the plug-in developer for assistance) it may be that the Quickmarks plug-in doesn’t support release 4.x of eclipse. I notice, on the SourceForge website, that there are only downloads for eclipse releases in the 2.x and 3.x series. Your log file may show errors when trying to install the plug-in. Note that there appears to be an equivalent plug-in (Quick Bookmarks) available via the eclipse catalog (go to Help->Install from Catalog…, then switch to the eclipse catalog before searching for Quick Bookmarks), so that may be an option for you.
I hope this helps.