I don't regularly use firefox, but that's for three reasons.
1. Every time I fire it up, for years, through multiple versions, I get:
"The update could not be installed. Please make sure there are no other copies of Firefox running on your computer, and then restart Firefox to try again." I have various plugins, some of which are active, some aren't. I have no idea what the problem is. When I first saw it, maybe two years ago, Firefox wouldn't start at all. Now it always starts, but not without that message first.
2. Downloading programs. I'm soo lazy that over the next I've never looked into this. But every time I download it puts my file into a download manager of some kind. I hate that. I just want it to save to my desktop or other location I pick, not automatically sit in some folder. Plus when I do go to download that folder is full of 80 other things I downloaded before. How do I just change everything to download to my choice of location the same way IE does? I.E. Save As
?
3. The number one reason I use I.E. is because of a instant search functionality called Searchy which is configurable at this site:
http://searchy.protecus.de/en/ For I.E. users this is amazing,and you can quickly create custom search strings to any site you want. For example, from the address bar, if I want to look up "amazing" in the dictionary I just type "dic amazing". The search string is customizable. I'm sure Firefox has an extention that will do this but I want to make sure it's done from the address bar (not the search bar), and that the search string is customizable. I have so many I've used for many years in IE that I'd want to configure firefox the same way.
So it's these three issues that really stop me from using Firefox the most. Other than that it's clean and great for web development with all it's extra tools, but until I resolve these three issues I'm sticking with IE.