Go to Tools >> Options >> General, see where your downloads are saved, then go there.

it was a empty file

Sorry, I think that as you turned off the computer the download before it complete the file was erased automatically by Firefox

But if you dont disable the history, maybe you can restore your previous session:

• Restore previous session

Did you look in the Downloads Manager?

• Firefox > Downloads
• Click the Downloads arrow on the location bar: Show All Downloads

• https://support.mozilla.org/kb/Downloads+window

i checked it but it shows me my downloads from yesterday

check firefox's default download location (under tools>options>general tab) it should say "save files to" with a destination

if they arent there try a search in windows, if you cant remember the file name search for all pictures of the filetype the website saves as (should be .jpg)

if you still cant find them, it may be that instead of saving them, you opened them directly, which potentially means firefox saved them in temporary files. if that is the case, they could have been deleted from the system

If you can't find them in Firefox (e.g. Downloads or History in the Library) and also not on the computer then I'm afraid that they are lost.

Note that they may have a wrong or missing file extension, so you can also check for files with a time stamp for around the time you downloaded the files.