AMO:Editors/EditorGuide/ThemeReviews

Themes

Themes have limited capabilities to run code, but this is generally not allowed. Make sure to run the validator to see if there is any JS in the theme. If there is, it should be admin-reviewed.
Go through all menus to check that the theme is complete.
Add a livebookmark to your bookmarks toolbar if you don't have one.
Go to an extended validation secure site like and a "plain" HTTPS site like wiki.mozilla.org. Make sure there's a clear distinction in the identity button for these two, and between the two and regular HTTP sites.
Check all the icons are there under View -> Toolbars -> Customize.
Open the History and Bookmarks windows, as well as the sidebars.
Make sure the theme looks good. Text should be easy to read and buttons should be clear and concise. As well as just looking stylish, make sure it all looks stylish in the same way.
Another important aspect of a theme is to make sure it "fits." This is relevant for menus and dialogs - check to make sure that all the UI elements fit within the default boundaries and do not appear "clipped". If anything's clipped and/or if resizing is required to see it completely, make a note of it and request the author to change it.
While testing a theme, don't forget to check that the author has included a suitable preview image.

All these URLs should be viewed

https://addons.mozilla.org, identity box with corporate name and distinctive color (make sure identity box detail drop down displays correctly with appropriate icons).
https://www.mozilla.org/, identity box with just domain name and distinctive color.
http://www.wikipedia.org/, identity box should look different than other 2 states.
https://mozilla.org, untrusted connection alert.
http://www.mozilla.org/en-US/firefox/geolocation/ (Test geolocation alert) - Click on link labeled "Give it a try" and then the "where am I" button to activate geolocation alert.
https://addons.mozilla.org/en-US/firefox/addon/classic-compact/reviews/ (Test RSS feed icon) - Place RSS button on toolbar and make sure its appearance is different for pages that have RSS feeds (like this test page) from those that don't.
about:home
about:config
about:addons

Tab strip scrolling (open enough tabs to force the tab script to scroll) - make sure it scrolls properly and has scroll arrows at each end of tab strip.
Pinned Tabs (verify pinned tabs function correctly)
Tab Groups / Panorama
Side bar (ctrl+B)
Customize toolbar (verify small and large icons function properly)
Customize toolbar (verify show: icons, icons and text, & text options function properly for both large and small icons)
Places (All History / All Bookmarks) - some themes break the toolbar buttons in these when set to small / large
Turn on all toolbars
Place tabs on top and disable menu bar, maximize and restore browser window. Ensure tabs display in title bar correctly when browser window maximized (Windows/Linux)
When menu bar is turned off, make sure window controls on right side of title bar (min/max/restore/close) display and function correctly
Web Developer tools (Web console, Inspect, Scratchpad, etc.)
Page Info
Private Browsing
Option. Make sure Options / Advanced / Network / Limit Cache > spin buttons are styled as well!
About Firefox - the logo should not be replaced (but a custom made logo can be added)

DOM Inspector (make sure the syntax highlighting doesn't make items unreadable - especially with dark themes
console2
Venkmann (Javascript Debugger)

The Theme should be usable without Mouse - widgets have to change their appearance when tabbed through them with the keyboard. (e.g. checkboxes, radio buttons, tabs, should indicate key focus)

Full screen mode - there must be restore and minimize buttons!
Tabs on Top - Tabs may be above the Address bar or on the Caption of the Window, this is a matter of choice for the Theme author
Try to move the search box to a different toolbar (e.g. menu bar); this is what people with narrow screens would do
Sync Now