hi, thank you for reporting this. could you capture & share a performance profile while this problem is occurring? maybe that can provide more clues as to what's going on and how to fix it...

https://developer.mozilla.org/en-US/docs/Mozilla/Performance/Reporting_a_Performance_Problem

I have perf.html up and it is recording. I cannot tell what to do next

you can start the recording with ctrl+shift+1. then reproduce whichever steps are triggering the slowness. after that press ctrl+shift+2 in order to capture the performance profile. it will open up in a new page. on the top right there you'll see a share button - please click it, which will provide you a link that you can share here in a reply on the forum.

Thank you. But the biggest problem is slowness when I open Firefox. perf.html is using Firefox, and I cannot load Firefox again once it is open.

I see that there is a way to run perf.html on startup by using special commands. I am not a Firefox developer or even a power user so I do not know how to do this. I could do it with your help if you have the time to walk me through it. Firefox has had performance problems ever since I changed to Windows 10. I actually got it running pretty well, finally, and now this. I would have changed to another browser long ago if there was another one with security that was as good. Firefox has far too many problems. I don't know why it is not tested better before release......this problem is a show-stopper and I may have no choice but to give up on it.

can you try to replicate this behaviour when you launch firefox in safe mode once? if not, maybe an addon is interfering here...

Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Good troubleshooting suggestion! It solved my problem. Thanks for continuing to help me out. But I do not know how it fixed it. I put Firefox in safe mode (the article did not state how to take it back out of safe mode, which I found very annoying!). In safe mode, Firefox loaded right up. So I disabled the add-on that I had added most recently, which was Gecko Profiler. Then I had to use Google to find out how to take Firefox out of safe mode. I found that to be really sure it's out of safe mode, I should reboot my computer. I did so, and Firefox loaded right up again......then I realized that Gecko Profiler was what you had me add, if I recall correctly.

So either Firefox is still in safe mode (I don't know how to tell) or else there was some other factor at work. I reboot often but not every night. It's possible that I didn't reboot after I updated to version 60, but I don't recall seeing a prompt to do so, either. I think it had the usual prompt to restart Firefox, which I would have done. So it's a mystery. Any ideas? In any case, because of you, I will keep Firefox, if it continues to behave. Thank you.

so far we've seen the addons "reddit enhancement suite" and "honey" perhaps implicated in these slowdowns in firefox 60. our developers are currently poking at the problem,hopefully they can come up with a solution within a couple of days - the work is tracked in https://bugzilla.mozilla.org/show_bug.cgi?id=1460636 ...

Upgraded to Firefox 60 yesterday, and it was *VERY* slow under Windows 7.

What seemed to speed it up was to disable Telemetry (about:telemetry), so there's possibly something there that needs to be looked at?

I've been looking thru many issues here; well basically on slowness and crashes; and just realized I saw something related to Reddit.com. The last few days I noticed if I had 3-6 Reddit windows open along with my Yahoo and Twitter, that everything turned to frozen molasses. All audio was like a picket fencing AM radio, Any video looked like a slide show set for 60 sec changes. GIFs were just a smeared abstract frozen mess. My CPU usage was nearly 95% Constantly and my Mem and Disk usage was pegged at 100%! About an hour ago, 8am today 6/27/18, I noticed in the upper right corner in Very Very pale blue lettering "Return to old Reddit" and clicked it for all 4 pages. Not only was the switch instantaneous, and BTW looks a heck of a lot better than the new version (Beta testing without warning I'm assuming) every other page I had open suddenly reloaded and every video started to play. I forgot I had the surround turned way up and caught me off guard. That; at least for me; seemed to fix the slowness, seemed to help quite a bit. There does still seem to be an issue with this version of Firefox though. My Mem and Disk usage went up nearly 40% with this version and there always seems to be an issue with embedded video playback. I mean, YouTube, Vimeo, Dailymotion etc... are all OK, it's the videos within Yahoo, FB, Twitter; seems like any social media site; are the ones that FF is having issues with playback. Sorry, that seemed shorter when I was thinking it but I just wanted to let you know what I found might help. I just need to add my O/S is Win10 and my connection is hardwired Xfinity cable internet.

I'm having the same problem: FF way too slow. None of the solutions I have tried have worked or the solutions are too complicated for the average user. I know if I screw up one of these complicated solutions or some clever person leaves out a step in instructions, FF will not be at my side to fix a messed-up computer. Hey, FF. If this problem is so pervasive, why not launch another update to fix your last update?

Until then, I will use Edge, which I hate but at least it works. I am sick of waiting 10-15 seconds for a page to load or for a cursor to appear in a message window after applying simple fixes. It defeats the fast connection I pay for. FF doesn't seem willing to fix this screw-up for everyone. Instead, they are making everyone fix their problem. One doesn't hear from those with permanently screwed-up comp. They just go to other browsers after their comps are fixed.