STR: - (to see a big difference navigate to a site with a responsive design) - Open console and enable CSS Log - Change the viewport (responsive design view tool or resize window) It will take much longer to render (doesn't matter if you close console or not)

(In reply to sjw from comment #0) > STR: > - (to see a big difference navigate to a site with a responsive design) > - Open console and enable CSS Log > - Change the viewport (responsive design view tool or resize window) > > It will take much longer to render (doesn't matter if you close console or > not) When we activate CSS Logs, we use reflow observers, so I guess it's expected to be slower, but not sure how much slower. But closing the console should remove all the observers though…

(In reply to sjw from comment #0) > STR: > - (to see a big difference navigate to a site with a responsive design) > - Open console and enable CSS Log > - Change the viewport (responsive design view tool or resize window) > > It will take much longer to render (doesn't matter if you close console or > not) Do you have an example of a website where it's very visible?

(In reply to Paul Rouget [:paul] from comment #2) > Do you have an example of a website where it's very visible? There is no specific site, but note this: (In reply to sjw from comment #0) > - (to see a big difference navigate to a site with a responsive design)

(In reply to sjw from comment #3) > (In reply to Paul Rouget [:paul] from comment #2) > > Do you have an example of a website where it's very visible? > > There is no specific site, but note this: > > (In reply to sjw from comment #0) > > - (to see a big difference navigate to a site with a responsive design) I tried. I can't reproduce.

(In reply to sjw from comment #3) > There is no specific site, but note this: > > (In reply to sjw from comment #0) > > - (to see a big difference navigate to a site with a responsive design) Can you suggest a website?

Maybe a simple flexbox demo: https://developer.cdn.mozilla.net/media/uploads/demos/S/J/SJW/6c8c9d12500ac1645675319313370eed/flexbox-chapter_1375972833_demo_package/index.html I was watching my CPU graph while testing: Normal: small peek Log enabled and console open: large peek Log enabled but console closed: large peek I think the performance is worse on more complex sites, but this demo should hopefully be enough to reproduce.

Erf, I really can't reproduce. Sjw, if you keep the console open and just uncheck the "Log" checkbox, do you still have this issue? I see how the page slows done when CSS>Log is activated, but in my case, unchecking the checkbox or closing the webconsole returns to normal.

There is may be a performance relation between these bugs.

OP: Did we ever determine if you had Reflow Logs enabled? Under the CSS filters, Reflows shouldn't be selected. Also, disable any extraneous logging, e.g., Network logs, full response bodies, etc. Have you noticed a perf regression since any of our recent changes have landed? Since around Firefox 28, 29? Any information would be helpful.

(In reply to Rob Campbell [:rc] (:robcee) from comment #9) > OP: Did we ever determine if you had Reflow Logs enabled? Under the CSS > filters, Reflows shouldn't be selected. > > Also, disable any extraneous logging, e.g., Network logs, full response > bodies, etc. > > Have you noticed a perf regression since any of our recent changes have > landed? Since around Firefox 28, 29? > > Any information would be helpful.

On my old hardware I still have performance issues, but on the new hardware it's trivial. (In reply to Rob Campbell [:rc] (:robcee) from comment #9) > OP: Did we ever determine if you had Reflow Logs enabled? Under the CSS > filters, Reflows shouldn't be selected. > By default they are not selected and everything works fine. If I enable the logs, the performance is worse when resizing the viewport. > Also, disable any extraneous logging, e.g., Network logs, full response > bodies, etc. > Other logs were not enabled. > Have you noticed a perf regression since any of our recent changes have > landed? Since around Firefox 28, 29? > I tested it before Australis landed on release. There is no noticeable regression.

If this was due to the number of logs coming through to the frontend, that should have been helped greatly by Bug 1237368. I also don't think CSS->Log is an option anymore in the UI.