text: I had the same problem for days.  In Yahoo Help menu, type in "I can't compose" and you will get a screen with that same question at the top of the page.  If you click on that question, it will take you to another menu which will tell you how to fix it.  I'll basically tell you what it says once you click on the question to fix it:\n\nIf you do not wish to change your browser, 1) you click the "Options" link on the top-right hand; 2) click "General Preferences" under the "Management" category; 3) choose the option "compose messages as plain text" under the "composing E-mails" section; 4) scroll to the bottom and click the "save" button.\n\nThis is thankfully what worked for me.  If you still have a problem, you can click the "contact us" button at the bottom of the page and ask Yahoo customer service directly.  I was going nuts so I wish you the best.