I have been seeing this for a long time now in Firefox, when I start up my machine and launch it it can take up to 45 seconds to launch, but if I close it and then open it again it will take a matter of only about 5 seconds. And this is always the case.
So why does Firefox take much longer to start on its first start of the day (I assume this is reset on every new startup of the machine and not day), but if it is closed and then started later takes far less time?
I assume that it must be reading/writing a lot of data on its first startup or something that it only has to do the first time?
I am running Ubuntu GNOME 16.04 with GNOME 3.20 and Firefox 47.