If you work from home and have to use a lot of web applications that are critical (VPN to work, or access on the web databases with big code loads), don't upgrade if you do not have to, or use IE for those applications if compatible. There's going to be a lot of application breaking with these rapid upgrades.
What? You didn't hear about it?
PC World will fill you in. 6, 7, 8, etc. are going to be coming out way faster than before.
In the meantime, if you aren't afraid of a new bleeding edge, upgrade. I use a bunch of older plug-ins not updated for a while (mostly blogging related), so I will more than likely wait a few iterations to see if any replacements for them pop-up on the Mozilla site. This is going to be very interesting. Not sure why they are aping the Google Chrome fast update cycle, but it might leave Apple Safari and Microsoft IE as the most stable browsers, which is bizarre, but very sci-fi like.