It would be better to create two profiles in firefox to separate work and personal. And both can be started at the same in two different browser instances if you like.
This, absolutely. What I mentioned as "work" above is personal work. Keeping work sessions, history and bookmarks separate is better (and probably safer?) than having all in the same browser. This issue is even bigger with Chrome if your work account happens to be managed, as it may take over your browser's settings.