Hi, please check in : SAFE MODE as no info came about your Extensions +

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

In Firefox Safe mode these changes are effective:

• all extensions are disabled (about:addons)
• default theme is used (no persona)
• userChrome.css and userContent.css are ignored (chrome folder)
• default toolbar layout is used (file: localstore-safe.rdf)
• Javascript JIT compilers are disabled (prefs: javascript.options.*jit)
• hardware acceleration is disabled (Options > Advanced > General)
• plugins are not affected
• preferences are not affected

TEST''''is issue still there ?

If nothing changes in Safe Mode please move to here : please try a Refresh but Note that this does more than uninstalling and re-installing does. Normal uninstalling does not remove some preferences which may have become corrupt. Please Refresh but do this 1st: Delete your Cookies and Cache and TEST.

• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

then

• https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

TEST....... If no issues then Extensions which need to be added back in 1 at a time and tested ..... Or it is your Profile : Make a new one and test ...:

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

If is your Profile :

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Note: Any customization will revert back to default, you will also need to reinstall Extensions.

Please let us know if this solved your issue or if need further assistance.

Hello MrMann,

In case the above doesn't solve the problem, here are a few other things to try :

In case you have 'Web Companion' from Lavasoft installed, would you disable it to see if that will make a difference  ?

If that's not it, then would you give this a try :

Type in the address bar   about:config  (press Enter) (promise to be careful, if asked) And reset all bold user set 'network.http' preferences to the default value via the right-click context menu and choose 'Reset'. At least check this preference : network.http.accept-encoding And make sure its value is   gzip.deflate

If that's not it either, then you could try this :

Type in the address bar about:config (press Enter) Promise to be careful, if asked) Type and look for the preference : security.sandbox.content.level and set its value to 1 (one) (default value is 3 )

Note : After you have made changes on the 'about:config' page, close and restart Firefox, in order for the changes to take effect.

Websites like Google and Facebook and YouTube have enabled Brotli (br) encoding for files send via a secure connection. Some (security) software intercepts a secure connection and acts like a man-in-the-middle to scan content and may not recognize this encoding and changes the content-type header to text/plain. This causes Firefox to display compressed content as gibberish instead of rendering the decompressed content. You can check the issuer of the certificate to see what software is interfering with the connection and places itself as a "man-in-the-middle" between Firefox and the web server. Make sure to have the latest updates of this software and possibly contact them for support.

See also:

• https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

A possible workaround (not recommended!) is to modify the involved pref and remove the trailing ", br" to prevent the server from sending files with Brotli compression.

• network.http.accept-encoding.secure = "gzip, deflate, br" => "gzip, deflate" (without quotes)

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config