hi, thanks for reporting this. could you go to the firefox menu ≡ > help ? > troubleshooting information page and take a look in the Accessibility section if accessibility is set to "true" there.

if yes, can you please copy & paste this whole section into a reply in the forum and see if the following fixes 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.

I tried to re-install using a different language version, and that seems to do the trick.

Updates to W10 yesterday appeared to direct hyperlinks to Edge rather than Firefox. Firefox was also behaving strangely over the last few days with early after daily start-up normal response speed, but slowing to crawl later in the day. Lots of TLS handshake info along with this snail's pace. Update of Firefox is normally transparent but then suddenly after W10, the classic "organisation policy --- blah blah etc" appeared in 2013 Outlook upon activating a link to browser. Uninstalled Firefox and reinstalled -- no change except loss of recent bookmarks. Found possible cause via Google the issue using the message from Outlook. M0S0kIM claimed a 1 minute fix and that was very close to the time. Regedit -- Hkey current user _ software_ classes_ html _ found Firefoxhtml _ changed to htmlfile _ job done.

I'm having different issues with this version on my iMac running 10.12.6 Sierra. A number of sites including the log in page for my Asus router are cut in half either horizontally or vertically which never happened on previous versions. The Android Central site, https://goo.gl/SvRJ27 loads and the left side immediately disappears. This is clearly a bug in this version and I'd like to request it gets fixed and SOON.

To thc4fox:

Updates or not, Windows 10 will periodically, under certain circumstances, change your default programs back to what IT (Windows 10) wants; so you have to go into Control Panel > Default Programs and change your default programs back to YOUR preferences.

I don't know what idiot at Microsoft designed Windows 10 to do that, but it's not a specific update that causes Windows 10 to change default programs. It's the way Windows 10 is designed. It does it intentionally, and it is not "faulty" code or an update that causes that behavior. It is intentional programming.

As for your Firefox behavior, there has been one flaw after another with Firefox from around version 55.0.3. I reverted back to that version after trying to use version 57 on Windows 10 pro 64-bit. Firefox's new design just didn't run well on Windows 10, and it didn't run as well on a 64-bit operating system as the 32-bit version of Firefox 55.0.3. In fact, NOT A SINGLE ONE of Firefox's 64-bit browsers has run well on Windows 10 pro 64-bit--or on Windows 7 Ultimate 64-bit. For some reason, the Firefox developers just can't build a decent 64-bit browser. There are always dozens of little bugs in the works that cause the browser to crash, stop responding, or some other failure--and usually at the most critical times.

To reiterate regarding the default programs, Windows is DESIGNED to DELIBERATELY discard your default choices and revert back to WINDOWS' default program choices, especially the default browser.

You will have to go in and redo all of your default programs. BE SURE, when you set the default browser as Firefox, to click the "Choose defaults for this program" link, then check ALL the "Extensions" and "Protocols" options so that Firefox is set as the default browser for them, and don't forget to click the "Save" button in the lower right-hand corner of the options window. Just setting Firefox as your default browser WILL NOT make it the default browser for all protocols and file extensions that it is capable of handling. Windows will try to pull a fast one and leave Edge as the default browser for HTTP, FTP, and HTTPS protocols, and HTM and HTML page extensions.

To Al, Thanks for the response. Actually I did the W10 default selection as you described before resorting to regedit. What was there was "FirefoxHTML" so changed that to "htmlfile" with immediate positive result. Some of the posts I read had similar stories in that the standard approach did not rest the default ex Outlook to firefox, but the direct edit did the job. On the 64 bit saga with Firefox: I was active on the Nightly release channel for over a year when there was no 64 bit Quantum etc.. Some odd happenings with that one, especially logging into https sites. Since firefox 64 bit came along, I have had little trouble until the last week or so with the loss of response and slowing down at the end of the day. Still prefer to MS browsers of any version so hope it settles in good shape.

Had less troubles all-round with W7 and of course I still wake up Linux Mint from time to time and the firefox version in that is completely trouble-free. Cheers. Terry