Update: Transparent Zen

[sameerasw]

Added new bg image feature for no tab page, more improvements with linux transparency toggle, new preview image and fixes, switched to -moz-pref, removed obsolete features, categorized options.

This pull request introduces several enhancements and updates to the "Transparent Zen" theme for the Zen Browser, focusing on improved customization options, animations, and user preferences. The most significant changes include replacing -moz-bool-pref with -moz-pref for better compatibility, adding a new "no tab screen background image" feature, updating preference labels for clarity, and incrementing the theme version.

CSS Updates:

• Replaced all instances of -moz-bool-pref with -moz-pref for improved compatibility with newer browser standards. (themes/642854b5-88b4-4c40-b256-e035532109df/chrome.css, themes/642854b5-88b4-4c40-b256-e035532109df/chrome.cssL1-R76)
• Introduced a new "no tab screen background image" feature, allowing users to set a custom image, control its size, opacity, and apply grayscale or inversion effects. (themes/642854b5-88b4-4c40-b256-e035532109df/chrome.css, themes/642854b5-88b4-4c40-b256-e035532109df/chrome.cssL109-R131)

Preference Enhancements:

• Updated preference labels with emojis and clearer descriptions to improve user understanding. (themes/642854b5-88b4-4c40-b256-e035532109df/preferences.json, themes/642854b5-88b4-4c40-b256-e035532109df/preferences.jsonL4-R104)
• Added new preferences for the "no tab screen background image" feature, including image URL, size, opacity, and filters. (themes/642854b5-88b4-4c40-b256-e035532109df/preferences.json, themes/642854b5-88b4-4c40-b256-e035532109df/preferences.jsonL4-R104)

Metadata Updates:

• Updated the theme description to highlight the new "no tab screen background image" feature and encourage users to explore additional features. (themes/642854b5-88b4-4c40-b256-e035532109df/theme.json, themes/642854b5-88b4-4c40-b256-e035532109df/theme.jsonL4-R13)
• Incremented the theme version from 1.11.2b to 1.12.0 to reflect the new features and updates. (themes/642854b5-88b4-4c40-b256-e035532109df/theme.json, themes/642854b5-88b4-4c40-b256-e035532109df/theme.jsonL4-R13)