This site will have limited functionality while we undergo maintenance to improve your experience. If an article doesn't solve your issue and you want to ask a question, we have our support community waiting to help you at @FirefoxSupport on Twitter and/r/firefox on Reddit.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

Cuireadh an snáithe seo sa chartlann. Cuir ceist nua má tá cabhair uait.

How do I stop Addblock Plus coming off each time I shut down and then having to reset everytime I turn on?

more options

"Adblock Plus could not be installed .. cannot modify file" was archived in 2013 but I'm still having the same problem over & over again. Each time I shut down my PC (WindowsXP) AdblockPlus is deleted and I cannot re-install without the daily ritual of resetting Firefox, downloading afresh & then re-installing. What can I do to avoid this?

"Adblock Plus could not be installed .. cannot modify file" was archived in 2013 but I'm still having the same problem over & over again. Each time I shut down my PC (WindowsXP) AdblockPlus is deleted and I cannot re-install without the daily ritual of resetting Firefox, downloading afresh & then re-installing. What can I do to avoid this?

All Replies (4)

more options

It is possible to download a fresh copy of the add on in a new profile:

more options

There are other things that need attention.

Your user agent shows that you run Firefox in compatibility mode for Windows 98 (NT 4.10).

  • Mozilla/5.0 (Windows NT 4.10; rv:37.0) Gecko/20100101 Firefox/37.0

Make sure that you do not run Firefox in compatibility mode. You can open the Properties of the Firefox desktop shortcut via the right-click context menu and check the "Compatibility" tab. Make sure that all items are deselected in the "Compatibility" tab of the Properties window.

more options

It is possible that there is a problem with the file(s) that store the extensions registry.

Delete the extensions.* files (e.g. extensions.json, extensions.sqlite, extensions.ini) and compatibility.ini in the Firefox profile folder to reset the extensions registry.

New files will be created when required.

See "Corrupt extension files":

If you see disabled or not compatible extensions in "Firefox/Tools > Add-ons > Extensions" then click the Tools button at the left end of the Search bar to check if there is a compatibility update available.

If this hasn't helped then also delete the addons.json file.

You can check for problems with preferences.

Delete possible user.js and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in the current Firefox release.


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

more options

Last fall, one release of Avast would delete your extensions at startup (http://www.ghacks.net/2014/11/16/latest-avast-reportedly-deleting-fir...). That was fixed long ago, but if you have any utilities that run at Windows startup, check to see whether they clean up any browser settings, files, history, etc. CCleaner may have features along those lines.