Extremely slow type/form rendering in Firefox 67&68 [Linux]

[flberger]

In all versions of the Firefox browser above 66.x I am experiencing extreme slowdowns handling the browser on a Gentoo Linux system. Apparently this is related to type rendering in forms, text areas, and the URI bar.

After typing the string "1234567890" as fast as I can, it takes around 5 to 7 seconds for the typed numbers to appear. They appear one by one, often with a second or more delay. Again, pretty much in every web form and in the URI bar.

I have tried the usual recommendations, using a fresh profile, a private window, disabling addons. Same effect.

I have had similar problems with the Qt based text editor "TeXStudio". All other applications, including GUI and input heavy ones like Mozilla Thunderbird and LibreOffice, work and render just fine.

Using top, I see that Firefox ramps up to ~50 % CPU when typing, along with X which also goes to 50-60 %.

I use a rather minimal XFCE4 desktop environment.

Currently I am staying on FF 66, which does not exhibit this behaviour.

Apparently

• Mozilla changed something in font / form rendering starting in FF 67
• It's something other applications are not affected by
• As it only happens in forms, it might also be related to spell checking (which I disabled) or some weird search in the background (which I tried to disable, too)
• It's a rare bug / condition, as apparently no one is reporting this. Might be some weird outdated library on my part?

I have little experience in tracking such a thing down. Where should I start? Any help would be greatly appreciated.

[therube]

Test in Safe Mode.

Have a different windows manager that you can test under?

If ? Hardware Acceleration is disabled, by default, in Linux, you might see if manually enabling it helps?
(Backup first.)

[flberger]

Test in Safe Mode.

I have tested in Safe Mode - same behaviour.

Have a different windows manager that you can test under?

I unfortunately can not. However, since it used to work up to 66.x, and all other applications are doing fine, I suspect changing the window manager is not going to change behaviour.

If ? Hardware Acceleration is disabled, by default, in Linux, you might see if manually enabling it helps?
(Backup first.)

It is disabled in my usual setup, but was enabled in Safe Mode. Results are the same.

I'd love to dig down into Firefox and see what it is doing when typing into text areas and forms. As CPU goes up visibly, it must be something computationally expensive, and it apparently has been introduced in v67.

[jscher2000]

Does it make any difference if you disable the form autocomplete features individually or together?

* Form history: https://support.mozilla.org/kb/control- ... rm-entries
* Address fill: https://support.mozilla.org/kb/automati ... -web-forms

[Grumpus]

Try disabling the Accessibility Services access on the /edit/preferences//privacy and security tab.
Also, are you depending on text from your own system or from offline, character sets offline may be slower than local (on your system)
Also are you having to convert from a pictogram alphabet to and standard character set.
You might want to review your settings in /edit/preferences/general/fonts & colors/ which "fonts for:" setting and alternate text encoding

[Grumpus]

One more thought - try and allow sites to use their own fonts instead of ones you call out in /edit/preferences/general/fonts & colors/
If using your own fonts it may also slow the process.