Am on a very sub-optimal laptop with a Celeron 1.73GHz processor and only 1GB RAM setup running Windows VIsta 32-bit and have been using an old version of Firefox (can't remember anymore - probably about v 51.0) which crashes often enough due to low memory and when browsing any website that is too "Flash"-y. I simply deal with this situation because that is what i have, i just avoid 'heavy' websites and can even get by using the Mobile Facebook site and 'Basic HTML' versions of Gmail. The Firefox update pop-up has been strongly recommending v.52.6.0esr which i have kept declining for the past few months. Today i finally "relented" and decided to accept the update because the crashes were getting more frequent. 1a) The update didn't seem to 'take' and the end result is the Firefox Shortcuts all lost their links, and i could also see the HTML files (lose their Firefox type icons). Checking the contents of Program Files confirmed that the fIrefox.exe was not there. 1b) Control Panel / Programs and Features, however shows Mozilla Firefox 52.1.2 ESR (x86) en-US but Uninstall is not possible, this is when i first encounter the Dialog box of "NSIS Error" - picture of same attached. 2a) Now i open Internet Explorer 7 and go to the Firefox download page - i go ahead and click Download Now on the main page and later confirmed that it got the FirefoxSetup 52.6.0esr.exe 2b) The same error appears - but the Setup Wizard was completed, reaching the last dialog box "... has been installed on your computer. Click FInish to close the wizard". 2c) The type icons have re-appeared but trying to run Firefox by clicking the old Shortcuts showed a MS-WIndows error "Firefox has stopped working" (Problem Event Name : APPCRASH) 3a) Restarting was no help, so i go back to the Firefox download page, and realize there are infact newer versions and decide to go ahead and download one - i choose Firefox Setup 54.0.1 3b) Download proceeds without problem, but double-clicking the Setup.exe results in nothing happening - even using "Run as Administrator". Am guessing i need to uninstall the old ESR version first - but i can't because of the NSIS Error. so now i am stuck - i don't know how to uninstall the old Firefox, even trying the helper.exe - picture attached. i do want to stick with Firefox and not use other browsers, because it works (did) well with my limited configuration, but i need help on how to proceed. Thanks. P.S. i have already found the Profile data to backup the bookmarks at least.