In your Firefox browser, if you cannot use CTRL+SHIFT+V to paste plain text without any formatting (paste special function), then one possibility is that you have a conflict with a Firefox add-on. A common conflict may be with the popular Firefox add-on AdBlock Plus. Edit preferences in Firefox to quickly fix this Firefox paste special issue.
How To: Firefox Paste Special Fix
If you’ve got Firefox and the AdBlock Plus add-on installed, then this solution may be for you:
1. In Firefox, go to edit your user preferences by typing “about:config” in the Firefox address bar.
2. Search or scroll down to the preference name “extensions.adblockplus.sidebar_key“, then double click on this preference.
3. In the pop-up window, change the string value from “Accel Shift V, Accel Shift U“, to replace “V” with another letter (ie. “Accel Shift J, Accel Shift U”), or else just delete the “Accel Shift V,” part completely (including the comma) so that only “Accel Shift U” remains. Then click OK.
4. Check the value for “extensions.adblockplus.sidebar_key” to see that your changes are correct and have been saved.
5. Restart Firefox.
You can test that the paste special feature is working properly within Firefox, by editing text in a Google Drive document, for example.
If the AdBlock Plus extension was the cause of the conflict, then you should now be able to use CTRL+SHIFT+V to use paste special in Firefox, without losing any AdBlock Plus functions. If these steps have not solved the problem, then it may be another Firefox add-on that is causing a conflict.