Windows 7: EMAIL encryption when using Firefox

I am trying to find a program that will encrypt my email (hence this forum vs. software). I need something SIMPLE - I would like to open Firefox, type in my message, click on ENCRYPT then have the program encrypt it so the receiving person can enter a key (which I have already provided) and then the msg would automatically decrypt. I have downloaded a few and they either needed keys/certificates (which I never received/downloaded); would not find the window in 'focus' so got "no text seen" msgs; needed true mail programs like Outlook or Thunderbird; could NOT make a self decrypting msg (once provided key was entered by the recipient <as they may not have the encryption program installed on THEIR computer>) and on....I really don't want to create the text in a Word window - encrypt it and then cut and paste into the Firefox msg window. Does anyone know of or IF such a program does exist?? Thought I had it in a program called Flexcrypt but cannot get it to encrypt as it is supposed to. ANY help or name of a program would be appreciated. THANKS...

Here is an easy in-browser solution:
https://encipher.it/
You will need to install bookmarklet into your browser.
Then type text, click bookmark, enter password, click Encrypt. Voilà.

Or you could just use the website.
Recipient may install a bookmarklet also or just use the website to decipher the text.

Thanks for responding.... Can I assume that you use this program or perhaps did? I must be doing something wrong. I must be doing something wrong and perhaps you can tell me what that is. I opened Mozilla Firefox, and then copied the link to my bookmark page as it states. I then go to Yahoo mail and then click on the NEW MAIL button and enter the name to receive the email, title, etc. I then type the body. When finished I click on the Encipher It 'button' and it says "message cannot be found". HOW can the msg not be found when I am in the mail create page and the text is right there???? ANY help appreciated. It seemed so simple! Thanks..

Hmm. For some reason it does not work for Yahoo Mail. However, it does work for dozens of other websites like Gmail, Facebook etc. Alternatively, you can use website's interface to encipher messages.

This may be what you are looking for: How To Encrypt Email Messages in Firefox