What's the difference between F5 and Ctrl-F5 in Firefox related to JavaScript events?

Ctrl+F5 clears the cached files in browsers where as F5 just refreshes the page but it uses cached files. Eg say you load a page make changes to a css file and upload it press refresh or F5. Page just refreshes and doesn't fetch the new revised css file hit ctrl+F5 it goes it clears the cache for the page and fetches the file again from the server. This would then load the new css file which would display the changes.

Firefox caches not only loaded files but changes made to page( user input and even changes to attributes made by JavaScript). Check this. So if your menu depends on some attributes you can just hard-refresh by clicking CTRL+F5.

ctrl+F5 will just force the cache to be ignored. Perhaps you have a subtle asynchronous-programming bug that is only surfaces when you have a faster page load (due to using the cache).