A few days ago I did a clean install of Ubuntu (15.10), and applied all updates. Everything seems to be fine, except an annoying issue with web browsing. I've seen the same issue in both Chromium and Firefox.
Frequently (roughly every 5-10 minutes), I request a page (via a link, or bookmark, or directly typing the URL) and the browser just pauses on that request. It doesn't hang - the browser is still fully responsive - just the request does nothing. With the developer tools open, I see the request appear as a row in the Network tab, but nothing happens. 2 minutes later, the request times-out, and the browser shows me its own error page, then (in the case of Chromium) it automatically refreshes the page and everything works fine.
If I manually refresh during the 2 minute period, I seem to just get another request that pauses similarly, although I have a feeling that if I refresh towards the end of the 2 minutes, it does seem to work; I haven't established a definite time period after which it always starts working.
The same thing seems to happen for all sites (at least, all those I've encountered during normal browsing - Google, Gmail, Facebook, this site, Amazon and various other online shops), I haven't tried with anything hosted locally, because I'm still setting up the box, so don't have anything running locally to test.
During the 2 minute pause, I find the same problem in other tabs, windows, and both browsers, but get normal responses when I ping the site(s) I'm waiting for, or any other site.
I don't think it's an issue on my home network, because 2 Macs and various mobile devices don't experience the same issue, although I do only have a cheap, ISP-provided router, so it is a possibility. I see the same symptoms on both a wired and a wireless connection.
Finally, I think the same symptoms are occurring for AJAX requests as well as those directly initiated by me - if I leave the developer tools open with an AJAX-heavy page (Facebook, for example), I see requests timing-out then working properly, just as I do when I click a link.
Although I'm a relatively comfortable user of Ubuntu, I'm far from any kind of Linux expert, so not really sure what to look at next to help me diagnose this issue. I appreciate that what I've included here probably isn't enough to get a simple answer, but I'd certainly appreciate pointers for anything else I can test, to get more useful information.