Hi As far as I am aware, you can use Firefox and Microsoft Office on the same computer without any issues. Firefox is a web browser, whilst Microsoft Office is a productivity suite. As for crashes, a lot of work has been done to improve Firefox. It is impossible to give a definitive answer as there are so many thousands of combinations of computers and software, but to give you an idea, I used a pre-release version of Firefox that is two numbers ahead of the current finished product for a year and struggle to remember the last time it crashed on me. I hope this helps, but if not, please come here and we can look into a different solution for you.