I think someone else just reported the same kind of thing: https://support.mozilla.org/questions/1122454

Could you try "the usual" if you haven't already:

When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Clear Firefox's Cache

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes. If you do not see the number going down on the page, you can reload it using Ctrl+r to check progress.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, try either:

• right-click (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "View Cookies"
• (menu bar) Tools > Page Info > Security > "View Cookies"
• click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "View Cookies" button

In the dialog that opens, the current site should be pre-filled in the search box at the top of the dialog so you can remove that site's cookies individually.

Then try reloading the page (and log into FB again). Does that help?

If that doesn't help, could you test in Firefox's Safe Mode? In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement? (More info: Diagnose Firefox issues using Troubleshoot Mode)

Do you want to experiment with turning off the Kaspersky feature of filtering secure browser connections, or is that already disabled? See the Kaspersky section of this article: How to troubleshoot security error codes on secure websites.

I thought that this had solved my problem because when I started Firefox in safe mode I saw the Facebook login page OK. However as soon as I actually logged in to Facebook all I saw was gobbledegook again. So problem not solved !

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History > Show All History" or "View > Sidebar > History").

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks and history and cookies and passwords and cache and exceptions, so be cautious. If you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

Can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website then data from that website will be saved once again.

Hi Sn0flake, did you try turning off the Kaspersky filtering? That seems to have worked in a few other threads about FB gibberish.

See also:

• https://forum.kaspersky.com/index.php?s=bbdfcf797a91bc90230472c52c4b103e&showtopic=351027

Bug 1271875 - Kaspersky's scanning of encrypted connections causes garbled Facebook page

Please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html

Hi, yes switching off the Kaspersky filtering did solve the problem. So the question is, since I have had Kaspersky installed for a year and a half now (& several months of Kasp 2016), why did it suddenly go wrong last night for bothe me and the other questionner ? Did something change on th FB webste or in Firefox. . or . . ? btw thanks for your quick responses. :-)

It's a complicated brew, but from reading cor-el's references it seems:

• Firefox 44+ accepts a new kind of encoding (compression) called Brotli for secure connections

• Facebook turned on Brotli encoding last night

• When Kaspersky passes through the filtered Facebook content, it removes the indication that the site uses Brotli encoding, so Firefox seems to treat it as unencoded

As a workaround, you can set Firefox NOT to tell sites it can read Brotli encoding. I suspect this won't slow your browsing down very much, and it will allow you to use Kaspersky filtering if you like. Please try this (I can't test it myself):

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste enco and pause while the list is filtered

(3) Double-click the network.http.accept-encoding.secure preference and edit as follows: delete the , br from the end so it just reads gzip, deflate like the preference above it in the list, and then click OK

Reference for this preference change working for another Kaspersky user: https://twitter.com/lildingus/status/730493386461982720

See also:

• https://developer.mozilla.org/en-US/Firefox/Releases/44#HTTP
• https://developer.mozilla.org/Web/HTTP/Headers/Content-Encoding

Yes, that works thanks again. I removed the ", br", switched on Kaspersky filtering, re-booted & FB reads OK.

Incidentally I have another problem . . maybe I should log it separately . . For some time I have been having problems with the Windows 10 "Start Menu" crashing - the problem is intermittent - but a knock-on effect is that when start up Firefox, I get a message that says "Firefox is not your default browser" and then I am taken to the Windows settings 'window' which shows clearly that FireFox IS my default browser !. . . See : http://answers.microsoft.com/en-us/windows/forum/windows_10-performance/windows-10-critical-error-your-start-menu-isnt/f1d2762d-ea75-47b3-a858-0d8567f84c5a . . I'll try the MS fix first