When composing an email I noticed that some of the letters need to be pressed twice. Please advise?

The problem above just happened a couple of weeks ago. When I typed words in the microsoft word it is okay, the problem occurs only when I composed email in yahoo page.When composing an email I noticed that some of the letters need to be pressed twice. Please advise?
1. Blow out or clean your keyboard. 2. In Compose you are using Java and lots of resourses of PC. You may need more ram.

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