It only appears that Mac has only a History Sidebar (command + Shift+H, Ctrl+H on Windows) and not a History List (Ctrl+Shift+H on Windows).

The History list would provide you with the ability to see the visited date and time in a column and sort on it. Where you could see if the cutoff points were exactly eliminating April at the beginning and missing data anywhere up to the end of April would tell that someone selected View by Date in the Sidebar and selected April and deleted it with the "Del" key or context menu.

I don't know of any way to bring it back except to view it if you have a backup of your profile you could create "test" profile and restore the backed up profile the "test" profile and view it there. More like for forensics than most people would want to do.

Even if you did that and immediately used command+Z (Ctrl+Z on Windows) it would ot have brought back the deleted history back.

i dont have windows..there is a history in the top menu bar..however, as i mentioned my only options are: today, yesterday, last week, may, or older than 6 months..but not april!!!

No matter what you see, you are not going to get history back, you can try to find out what you are missing and how you lost it and try to avoid doing that again.

You told me what you see in the Menu, but you need to see what is in the History sidebar to make sure that what you see in the menu is the same, and you want to see exactly what dates are missing -- well at least it was a thought that it might help you find where it went wrong try to avoid problems in future.

The Mac command key ( ⌘ ) is generally the same as the Windows Ctrl key. Windows Alt key could be either Mac Cmd or Mac Opt key. I also supplied the Windows shortcut keys for the benefit of Windows users and because that is what I am actually familiar with but I can see what is in the Keyboard shortcuts list for a Mac at https://support.mozilla.com/kb/Keyboard%20shortcuts#os=mac&browser=fx4

As I see you have a History sidebar (command+Shift+H) on a Mac or in other words ⌘ + Shift + H

You want to make sure that you do not clear you browsing history nor your form history -- http://img232.imageshack.us/img232/4928/clearcachew.png