By using Process Explorer or Process Hacker or maybe task manager, I hope you can also verify that Firefox consumes a few GDI handles per open tab. Windows has a global limit and a per process limit of 10000. GDI objects are used for windows, for the file save dialog and also for user interface elements like buttons or lists. However many applications like Firefox draw everything themself like XUL etc. But still, Firefox consumes 3 handles for me (verified on another computer) per open tab. If you have a lot of tabs open (for reasons not to be discussed in this topic) this can be problematic. If it reaches 10000 windows will not create more. Sometimes firefox hangs, but often Fullscreen (e.g. youtube videos) will not work and the gui will disappear. Also the context menu will not open and the save dialog cannot work and is hidden. Am I the first to report this? I did not find anything. Can this be fixed? Can I post this to bugzilla? Can anyone confirm this? The latest version does not fix it.