Firefox 19.0.2; on Windows XP Pro Service Pack 3 build 2600.xpxp_sp3_gdr_130105-0416. I normally work using minimal privileges - so the user from which I mostly run Firefox doesn't have sufficient privilege to install a Firefox update. Now and again I log in as a privileged user, start firefox, and grab the latest version. However it happens quite frequently that Firefox goes into a mode where on Firefox startup I get an error window saying that it failed to install the update. When that window is dismissed, Firefox starts up and of course it's the latest version. Nothing I have tried appears to have any effect on this, but always after some period of time - in which I will have logged in and out a few times and probably started and stopped Firefox dozens of times - for no reason that I can discern it stops producing this error message and begins to start up without the error. This lasts a few days, and then it reverts to getting the error message. In case it's useful to anyone, the error window is labelled Dh'fhàillig ùrachadh a' bhathar-bhuig which translates roughly to "The software's update failed" and the text in the window is Cha do ghabh an t-ùrachadh a stàladh. Dèan cinnteach nach eil lethbhreac eile de Firefox a' dol air a' choimpiutair agad is ath-thòisich Firefox an uairsin is feuch ris a-rithist. which is roughly "The update couldn't be installed. Make certain no other copy of Firefox is running on your computer and then restart Firefox and try again". I have of course done what the window tells me; it has no effect (if it had that would mean the OS security was broken) which is a good thing but suggests that the message in the window is a bad thing. I also tried updateing from the Firefox help menu (and was relieved to see that didn't work). Using a priileged user to install the update gives the unprivileged user the latest version, but doesn't ,ake the startup message go away. I have a suspicion that what is happening is that Firefox running in unprivileged mode finds a security update, downloads it, and fails to install it, instead of recognising that it's running in unprivileged mode and just warning the user than an update is available; once it has done that the update remains downloaded in the unprivileged user's space, and even when the update is installed by the privileged user so that all users now have the updated version Firefox tries to install it despite its being already installed whenever the unprivileged user starts it up. If so, that would be a rather unpleasant problem, since it would tend to encourage people always to login with sysadmin privileges.