Firefox is excellent, but by default it loads pretty slowly. From an architecture/engineering standpoint, this is a good thing because (Unlike Internet Explorer) this means that Firefox does not keep things in memory when it's not actually running.
However, from an "I just want to use the thing" point of view, it's really annoying, especially when you open and close Firefox many times a day. Every time you start it up, it has to load EVERYTHING up before it starts working. This leads to rather slow load times, compared to Internet Explorer, which already keeps itself in memory when you are not using it.
If you just want to use the thing, and you've got lots of memory on your machine, then there's a simple trick to tell Firefox to keep itself in memory after closing the Firefox window.
In the Firefox shortcut (This seems to work for both Windows and Linux versions, and perhaps all versions, although I do not have anything else to test it on.), after the part that loads Firefox, add "/Prefetch:1" to it. On the windows version it would look like:
"C:\Program Files\Mozilla Firefox\firefox.exe" /Prefetch:1
in the "Target:" field. (Right click on the Firefox shortcut and select Properties to get the target)
Hit OK to properties, then load Firefox normally by clicking on the shortcut. First time you do this, it's going to load just as slowly as always. But after Firefox loads, close it. Once it's closed, open it again - You'll see a dramatic improvement in startup time, usually below 2 seconds.