Now that we determined that the OS/browser isn't the issue - go to Dell's website and get the most current driver for your wi-fi adapter - see if that helps the problem.
Hi! I also have a DELL laptop, and it too, is seriously slow with wifi.. I have a Latitude E6510, with all (so it seems) drivers up to date...
I suspect it to be a driver fault...
I`m gonna try a bios update when I get my new battery in the mail. Now, im currently without battery, use only the AC-adapter at the moment.
If that has anything to do with it, I would feel realy stupid. hehe..
Pretty sure, that`s not it.
Maybee its time to replace the wifi chip??
I`ll give it a go, and return here with more info.
The laptop is beginning to get old... like 3 years now. But, all the laptop`s I`we owned, had a good lifespan. Im sure, that if you take good care of you stuff, then you will have it for a looong time!