My wireless network works fine at home, but on some other networks it takes a lot of time to connect. If it does connect on these then I cannot get any DNS replies.
I suspect the wireless module. The adapter is 12:00.0 Network controller: Broadcom Corporation BCM4313 802.11bgn Wireless Network Adapter (rev 01). The module in use is wl.
This suggests that wl is incorrect for your device: Installing Broadcom Wireless Drivers I suggest you remove the driver package:
sudo apt-get purge bcmwl-kernel-source
Reboot and see if the native driver brcmsmac does a better job.
There is actually more than one adapter with that model name. To find out which one yours is type into terminal:
lspci -vvnn | grep 14e4
My netbook running 14.04 has a broadcom 4313 with 14e4:4727 (rev 01), and what I've done with this adapter (which isn't nearly as pesky in 14.04 as before) is for 4727.
Definitely purge bcmwl-kernel-source as mentioned if you went into "additional drivers" ... unfortunately this isn't always reliable. I don't use additional drivers anymore.
I installed linux-firmware-nonfree, which was a mistake on my part. If you installed it yank it.
Follow the steps here:
http://ubuntuforums.org/showthread.php?t=2226102&p=13076641#post13076641
I've had lubuntu 14.04, xubuntu 14.04, and now LXDE (14.04 based) and it's worked every time.
