Hi, Developer Edition shares your Profile (bookmarks for sure) with Release version Firefox. So please do this just in case :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Myself I do not know the answer but someone will see this or post back.

Here is a screen shot

You could ask about that in the Adblock Plus support forum. http://adblockplus.org/forum/

My question is not so much why is it appearing but why, when I uncheck the box it disappears but then is back on next opening of dev tools. Why have a check box that doesn't seem to have the intended effect.

Note that its not confined to Adblock Plus. The same applies to, say, aXe (accessibility add--on).

Adblock plus problems is to contact their Support for the problem. As to other addon problems those will be for those Addons to give support for.

Kim_Hughes said

My question is not so much why is it appearing but why, when I uncheck the box it disappears but then is back on next opening of dev tools. Why have a check box that doesn't seem to have the intended effect. Note that its not confined to Adblock Plus. The same applies to, say, aXe (accessibility add--on).

As said, it shares your Profile in the Standard version and if the standard version has it enabled then so will the Dev. I have both versions running and I never installed Extensions in the Dev but they are there, I never imported my bookmarks to the Dev but they are there. If you uninstall the dev or it has a issue with a update since updates every 2 days or so and it mucks with your bookmarks, they will be mucked up or missing in the Standard Release so back up as per URL's in previous answer.