Download Adbock plus here: https://addons.mozilla.org/en-US/firefox/addon/adblock-plus/

See the "Corrupt extension files" section of the following article.

• Unable to install add-ons (extensions or themes)

That's where I got it from and it installs properly. But as soon as I close firefox and re-open it, it's gone and I have to download and reinstall again

Have a look at: How to fix preferences that won't save

amitshree and Gingerbread_Man,

Thanks for your help.

I followed the instructions and it partially worked. I deleted extension.sqlite (it was the only one there from the three referenced in the instructions), deleted the file preference and i also deleted the folder adblockplus. I don't have to reinstall it anymore after closing firefox, it stays under extension. But it does something weird. Although it is still in the add-ons (extensions), and it shows as enabled, it's not functioning unless i disable it and re-enable it.

Did you also delete the compatibility.ini file to make Firefox rebuild other files in the Firefox profile folder?

Did you try to uninstall and reinstall ABP?

I had the same problem for a while. I start Firefox, but Ad-block was gone from my display. The add-on was there, just not working. This link is what I did to get Ad-block working again;

https://adblockplus.org/forum/viewtopic.php?f=1&t=14092&sid=9d62ebd699e6e79646bacb432bad9be9&p=73455#p73455

Thanks fredmcd. I reset firefox, reinstalled adblock plus and it's working fine now.

Glad I could help.