AppleScript check if Chrome Extension is installed
Google Chrome's AppleScript Dictionary doesn't have a direct method to check for extensions, so you need to test for the Adblock Plus extension in a different way.

If the Adblock Plus extension is installed, then the adblockplus.js file will exist within the "$HOME/Library/Application Support/Google/Chrome/Default/Extensions/ directory structure. So I'd test for its existence and the example AppleScript code below does that.

set fileExists to do shell script "find \"$HOME/Library/Application Support/Google/Chrome/Default/Extensions\" -iname adblockplus.js 2&gt;/dev/null"

if fileExists is not "" then
    display dialog "Adblock Plus is installed." buttons {"OK"} default button 1
else
    display dialog "Adblock Plus is not installed." buttons {"OK"} default button 1 with icon caution
end if