Does Salesforce1 support custom buttons?
I do want to point out the following.
Custom buttons do seem to work in the following scenario: (I have 2 of these buttons in my current project)
- custom button
- display type : detail page button
- content source : visualforce page
These DO show up in Salesforce1 when adding them to the page layout.
So in this case, the on-click javascript functionality could be moved to a visualforce page (nicer anyway) and that should work.
Salesforce1 doesn't support custom buttons, but you might consider moving that button's functionality to a Publisher Action, which is supported in both the web GUI and in Salesforce1. (This is assuming your custom button is a detail button.)
Publisher Actions are clearly SFDC's preferred method for adding capabilities to a a record detail page going forward.
As noted, Salesforce1 does not support custom buttons. However, Salesforce1 does support Custom Links. You can get the same functionality as your custom button, but it will be displayed at the bottom of your page. If you change your Detail Page Button to a Detail Page Link and add it to your Page Layout, it should appear at the bottom of the record in the Custom Links section.
EDIT: For the sake of completion, I do go back and verify that On-Click Javascript Detail Page Links do not work. When I switched back to URL, it immediately displayed.