I've had this issue on and off where I'll be browsing the internet just fine, go to open a new tab, and when I click over it gives me the "we're having trouble finding that site" message even though I'm connected to the Internet. Usually I'll just spam the refresh button, and it loads the page just fine in another minute or so, so it's not that specific websites are being blocked. This issue actually went away for a little while and then came back after I had uninstalled and then reinstalled Firefox yesterday (I was having an issue where the Firefox icon would pop up twice on my taskbar, which now seems to be resolved). But now it seems that Firefox is intermittently losing internet access, and I'm pretty sure I've tried to troubleshoot this before and didn't get anywhere with it.