In only the last week or two, I got bit by this. Suddenly, the browser tab would all but freeze upon switching back to tabs with search results, or searching again with new terms, or refreshing such a page. As soon as the page is completely loaded or reloaded re-displayed, within two seconds, it stops updating the mouse pointer when hovering over links. It still scrolls, but the rest of the page, everything not in the vicinity of what was already showing, is just white space. After thirty seconds of doing nothing, the browser warns that a script is slowing it down and offers to make it stop. If I wait, after thirty more seconds, it resumes functioning.
The CPU is AMD FX-8320 with 8 cores, of which only one gets completely stuck on grinding the script. I don't know if there's a profiler in my browser (Waterfox Classic). But I opened the console and watched while I made it stall again, and the last script to be loaded was GlanceCobrowseLoader_4.17.0M.js.
So I blocked that entirely using UBO and now things are back to normal. I can absolutely do without it-- it is apparently part of a tool called Cobrowse which according to its publisher is used for support calls or similar:
"Glance Cobrowse sessions allow one or more customer service agents to view the web browsing activity of visitors to a website. Agents see exactly what a visitor sees in their browser, with the exception of the contents of designated masked fields."
Ugh.
The very first thing I tried was changing the number of search results from 240 down to 120 and 60, and to my disappointment, the stall period was shortened from 70 seconds to 20 and then to only several. That told me there is probably something in some javascript which is running over all of the elements on the page and comparing them each to all the other elements, or otherwise operating upon them with respect to all the others. It seems to be an "accidentally quadratic" bug. It means the CPU load and time spent increases exponentially in proportion to the number of elements in the set, and not linearly. It is a well-known, oft-recurring failure in algorithm design. Indeed, every eBay page stalls for at least a moment before redrawing when switching back from another tab-- but none of them have nearly as many unique elements as search results.
On the other hand, it might not be an accident. It might just be a bad design based on questionable goals from the start. Anyway, this is shameful. Here's a pro tip: Stop making everything MoreBetterer, and it will stop getting worse.
