Windows marks the wrong text

Sometimes, if i try to mark a word or some text in firefox or somewhere else, windows seems to mark the text and the words, that i didn't select with my mouse. It makes it hard to mark the right text sometimes.

Selection? Try checking/changing your mouse. If you're using a wireless mouse, some users have had great difficulty with certain of these- even replacements.

It's not a mouse problem, it's something related to windows i think, or possibly my browser.