Is this about the browser.urlbar.autoFill pref or another pref like browser.urlbar.autocomplete.enabled? See "Prevent Firefox from automatically completing URLs":

• https://support.mozilla.org/kb/search-your-bookmarks-history-and-tabs-awesome-bar

You can check for problems with preferences and try to rename or delete the prefs.js file and possible numbered prefs-##.js files and a possible user.js file to reset all prefs to the default values.

• http://kb.mozillazine.org/Preferences_not_saved
• http://kb.mozillazine.org/Resetting_preferences

I have set both of the urls you refer to to 'false'. Each time I restart Firefox one or other seems to revert to 'true' so that the autocomplete function is enabled again.

Changing the preference in the Tools menu seems similarly not to 'stick'..why???

Hello johncastree, see and try the second session in cor-el reply > .......You can check for problems with preferences......values. Preferences not saved/Resetting preferences.

thank you

Mmm I think this may be beyond me...

Do you have a file user.js in the Firefox Profile Folder that may be causing the setting to change after a Firefox restart?

You can use this button to go to the Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder

You can start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do not click the Reset button on the Safe mode start window or otherwise make changes.

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

You can use one of these to start Firefox in Safe mode:

• On Windows, hold down the Shift key while starting Firefox with a double-click on the Firefox desktop shortcut
• On Mac, hold down the Options key while starting Firefox
• Help > Restart with Add-ons Disabled

Thanks for the suggestions. I have checked ..there appears to be no file user.js. There is a file user that appears to have nothing in it. I also restarted in Safe Mode and tried to reset..still I get autocomplete working when I restart,. Would there be any sense in simply resetting Firefox to default??

Windows may be hiding the .js file extension.
You can check the file type in the properties of a file via the right-click context menu.

Did you try to remove the prefs.js file(s)?

If you can't fix it in your current Firefox Profile Folder then you can try to reset Firefox or create a new profile yourself as a quick test.

• https://support.mozilla.org/kb/Basic+Troubleshooting

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

I've given up trying. Reset Firefox from the Troubleshooting tab and it seems to have sorted things...at least for now! Thanks for the help!