I've recently been experiencing occasional 100% CPU hangs when typing into the address bar, forcing me to kill and restart Firefox. Worse is that from that day forward typing the same two or three character sequence into the address bar will cause Firefox to hang again. It turns out this happens after you visit a very long URL, when you later type into the address bar an the suggestion list tries to include that long URL. In my case this most recently happened after visiting a reftest-analyzer link from TBPL results. More specifically for a Windows "R" failure from: https://tbpl.mozilla.org/?tree=Try&rev=cc042860ee89 The URL was almost 8 MB in length, and we end up hanging in text run code trimming white space when I type "que" into the address bar. To stop the hangs from occurring I had to figure out which long URL I had visited and then go into |History > Show All History| and search for and delete that URL so that it would no longer appear in the address bar suggestions list.

This is in a release build.

While limiting the length of the autocomplete results would prevent us hitting this bug, this issue should be considered separately. Something is rotten in the textrun code if we're hanging on 8 MB strings.

Yeah, that sounds like we have an inefficiency somewhere. Could you grab a profile of the hang?

Bug 907001 is on file for essentially the same issue, but is currently a front-end bug tracking limiting the results we display.