This is a pain but I have resolved it. This is instructions for Windows 7 but it may be the same on other Operating systems. Note: "''YOUR USERNAME''" relates to the account you log on to Windows with. # First go to control '''panel / folder options''' and ''uncheck'' ''''Hide extensions for known file types'''', ''check'' ''''Show hidden files and folders'''' and ''check'' ''''Show hidden operating system files'''' then click ''apply'' and ''OK''. # Go here :''' C:\Users\"YOUR USERNAME"\AppData\Roaming\Mozilla\Firefox\''' and copy the '''Profiles''' folder to your desktop. # Go here : '''C:\Users\"YOUR USERNAME"\AppData\Local\Mozilla\Firefox\''' and copy the '''Profiles''' folder to your desktop. You will need to rename this as you already have a Profiles folder so name it '''Profiles2'''. # Uninstall Firefox (''selecting to remove all user settings'') then go here: '''C:\Program Files\''' and delete the ''Mozilla Firefox'' folder. # Go here : '''C:\Users\"YOUR USERNAME"\AppData\Roaming''' and delete the ''Mozilla'' folder # Go here: '''C:\Users\"YOUR USERNAME"\AppData\Local\ '''delete the ''Mozilla'' folder. # Open another browser (i.e.'' Internet Explorer'') and download and install ''C-Cleaner'' here: [http://www.piriform.com/ccleaner/download/standard] # Once installed run the ''''Registry cleaner'''' over and over until no problems are detected and exit the application. You may now uninstall it but it is probably one of the best free apps available as it has a better uninstaller than Windows does and controls which programs run when Windows starts without using the 'msconfig' command. # Now download the latest version of Firefox with your other browser and install it then run the application once and close it down. # Open the ''Profiles'' folder on your desktop and inside you will find one or more folders with a name ending in '''.default''' (i.e. ''uomifhku.default''). Right click each folder and select '''Properties''' to see which contains the highest amount of data or the bigger file size. Once you have done that open the largest folder and make sure there is nothing in there with '''... @security.compass''' written on it. If there is then delete it. Hold your ''left'' mouse button and move your mouse pointer over all of the files to highlight in blue. Put your mouse cursor on any one of the files, ''right click'' and select 'Copy' to copy them all to system memory and then close the folder. # Go here: '''C:\Users\"YOUR USERNAME"\AppData\Local\Mozilla\Firefox\Profiles''' and find the folder ending in '''.default''' then open it. Now ''right click'' anywhere on the background in the main Payne containing the files and select 'paste'. When prompted to '''Overwrite Files''' and '''Merge Folders''' always accept and proceed. Once done, close the window. # Open the '''Profiles2''' folder on your desktop and inside you will find one or more folders with a name ending in '''.default''' (i.e. ''uomifhku.default''). Right click each folder and select '''Properties''' to see which contains the highest amount of data or the bigger file size. Once you have done that open the largest folder and make sure there is nothing in there with '''... @security.compass''' written on it. If there is then delete it. Hold your'' left'' mouse button and move your mouse pointer over all of the files to highlight in blue. Put your mouse cursor on any one of the files, ''right click'' and select '''Copy''' to copy them all to system memory and then close the folder. # Go here : '''C:\Users\"YOUR USERNAME"\AppData\Roaming\Mozilla\Firefox\Profiles''' and find the folder ending in '''.default''' then open it. Now right click anywhere on the background in the main Payne containing the files and select '''paste'''. When prompted to '''Overwrite Files''' and '''Merge Folders''' always accept and proceed. Once done, close the window. Start Firefox and if all is well you should be working again and it back in the state you left it last without the bug. Many thanks, sparkyuiop