Editing Problems

Editing Problems with Apple OS X 10.10.3

when i attempt to edit the text in a comment that i posted

if i try to high light part of it ........

everything on the entire page becomes grayed out

and then reverts back to the original page

without allowing me to make an edit

this has been going on for some time

when i am preparing the original post this problem does not happen
only when in editing mode

and it happens on my iMac as well as my macbook air

anyone else experiencing this ????

any tech advice ?

Thank You!!!

I didn't find the right solution from the Internet.
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