My some remarks about your last version:
1. about.js file is redundant - all code for about window is built in Firefox (credits for Ben are also redundant)
2. <!ENTITY ahs.prefs.height "520"> This entity is redundant - without this, window will be going to content
3. <!ENTITY ahs.prefs.showback.width "60"> This entity is redundant. This value should be hardcoded because set width for column with textboxes - finally set textboxes width. This textboxes have to have width for 4 digits - can be hardcoded.
4. width="&ahs.prefs.width;" This attribute should be 'minwidth' - when translation will take more place, window will be going to content, with 'width' is constant. IMHO you can use hardcoded 'minwidth' attribute as in the mine version so entity for this attribute will be also redundant
5. class 'spacer.halfAnEmHeight' is redundant - not used in the recent code
6. For buttons in the Debug log pane you used 'pack="end"' attribute and on the right side we have IMHO to many buttons - should be 'start'
Finally, you don't accept my change which add tooltip for tree content. IMHO this tooltip should be. Why? I long time thought how remove URI from list. With this tooltip all is clear. If you don't want add tooltip, add button for remove URI from list.
Below is Polish description for AMO.