hi, thanks for reporting this. can you try if this change can workaround the performance problem?: go to the firefox menu ≡ > options > privacy & security panel and under permissions check the setting to prevent accessibility services from accessing your browser.

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

.0.3 was running perfectly. .0.4 update is EXTREMELY sluggish up to hardly working. Typing this took me 8!!!!! times longer due to keyboard lag.

How do I revert to .0.3?

Addendum: Movies run extremely laggy. Other tings as well are very delayed, and laggy. Oddly, menu does act fairly normal speed wise, which makes no sense.

Furhter on, my entire system seems to be affected by this, speed and smoothness are no longer what it was.

POSSIBLE SOLUTION:

I restored my Windows 10 Pro x64 from an Acronis Backup. I added a few things, I fired up, stupid of me, Firefox which of course updated, and... it worked.

Now, what went wrong before: the installation I Had before I set back my backup had several things added (non related programs which I re-installed as well).

In my case I am absolutely sure it is Ant Downloader, due to the fact that my current installation now virtually identical to the previous installation regarding programs, save for this Ant Downloader.

Of one, Ant Video Downloader.

Now, V3.1.24 was made for FF57.0.3 and I had it running on 57.0.3. However, the update (NOTE: IN MY CASE!!!) caused a conflict with 57.0.4, creating hell on my system (which is why I reverted to my backup, the issues drove me insane).

My suggestion: removing Ant Downloader will not fix the issue (tried this). Installing 57.0.3 will not work either (left over stuff in various places like Registry???), tried it. Registry Clean (with CCLeaner and RegEdit, both run as Admin) did not fix anything either, in fact it got worse. All I could do was in fact go back to my old trusted Acronis Backup of my Windows installation (which I made like 4 weeks ago).

Before however you do a thing like this, make SURE all stuff you cannot have lost/deleted, to store it safely Also make a copy of your FF PROFILE FOLDER, but first make 1000% sure you removed Ant Downloader (not just deactivate, but REMOVE)! How to: OPTION 1: in FF, go to the three stripes icon top right, and choose Troubleshooting Information, in there click Open Folder at Profile folder, copy this to for example a, USB- stick.

OPTION 2: in the address bar, type "about:support" without the quote marks, then hit enter. Choose Troubleshooting Information, in there click Open Folder at Profile folder, copy this to for example an USB- stick.

OPTION 3: Open Windows Explorer and head to C:\Users\Admin\AppData\Roaming\Mozilla\Firefox\Profiles\, copy that folder to for example an USB-stick.

Upon having a new Windows installation (or restoration from a backup like I did) you install FF 57.0.3, load it, go back to the new PROFILES FOLDER and copy the content from your backup folder into the new PROFILES FOLDER (you need to actually copy it's content from within the copy into the original new folder: dragging the folder over will not help unless you have an identical named PROFILES FOLDER which would be quite surprising). This PROFILES FOLDER will be named something like blahblahblah.default.

Maybe someone knows a shorter way to copy the PROFILES FOLDER content to the new installation, but this is how I work...

Good luck, people.

And happy New Year!!!

EDITED FOR 2 TYPOS.