If the problem comes and goes it's probably not a browser setting, since that wouldn't change by itself every few days.

It's possible that it has something to do with internet issues on your way to PC, though I don't understand why one browser would be able to connect successfully when another couldn't. Just out of curiosity, what are you two seeing in the status bar when the problem is happening?

Did you happen to see what DocJohn posted last time we discussed slowdowns?

----------- Too much tech info, probably ------------

Long ago, at another site using very different software, I discovered that it made a difference whether people arrived there with or without a "www" in the site URL. Either way would get them in but it would also set their login cookie to that version of the URL. If they clicked on a link that someone had posted using the other version of the address, they'd find themselves mysteriously logged out. It seems unlikely that anything like that would be happening for you in this day and age but in the interests of leaving no stone unturned, would you mind checking whether you're using exactly the same URL for PC on both browsers?

Once (also long ago) I suddenly found myself unable to connect to the Internet. It turned out that there was a setting (in Windows, not my browser, I'm pretty sure) for what nameserver to use for looking up the routes to websites. Something (malware, perhaps) had changed it to something that wasn't even a nameserver. Resetting it to let my ISP choose the nameserver cleared up the problem. I think the same setting affected access with all browsers, so that probably wouldn't be your exact problem either.