I have been using Firefox for about 8 years. I'm using version 43.0.1 currently. Earlier on, many versions ago (like when it was 12 or 13) there were some locking up problems and it would reboot the software then pop back up after it fixed whatever was wrong, but I haven't seen that for at least 4 years or so now.

I don't use Firefox for email but use their Thunderbird dedicated email software instead. It's similar to Outlook Express but much more versatile.

Use Thunderbird for your email and you won't have those problems. It will even go to your mail server and try settings until it gets the right ones for you to sign in so that you don't have to enter any of the archaic pop.whateverserver.com or anything else. I have 8 email accounts at three different server companies and never have any problems except when one of the server companies is having a problem themselves.

After you get used to it, you won't ever go back to Internet Explorer and Outlook Express. You can also put a small app in Firefox called Adblocker Plus and never see ads on any webpages anymore. Backgrounds are customizable, screen colors are customizable, everything can be personalized to make a much more enjoyable browsing adventure.

I also use Google Chrome for browsing sometimes. No reason but I just like to use it for some stuff. Probably because of their Google Apps first page when I open Chrome.