In one of our project I was using Sitecore 8.0 150621 revision.
And I was getting an issue on Experience Editor for a non-admin user, user unable to see Add Here button when click on component button on tab panel.
So I decided to search the cause of this.
I found below link about this –
The Add here button was not displayed for the MVC placeholder in Experience Editor for a non-admin user. This has been fixed. (51676, 435944)
So we decided to ask this from Sitecore Support and got the answer from there –
There is no easy way to fix it by implementing a patch, however, as a workaround you can grant your user the write-access to the /sitecore/layout/Placeholder Settings/* items: http://screencast.com/t/tHvPOC6PZTSq.
After doing this our issue was resolved.
Happy Coding 🙂