# Description Sidebar-based addons can provide tooltips via HTML's "title" attribute same as webapps, but now it is shown with unstyled appearance - default font size and transparent background. # Steps to reproduce 1. Start Nightly 63.0a1. 2. Install Tree Style Tab (or something other addon providing custom sidebar panel.) 3. Show the sidebar panel for the addon. For example, hit F1 key for TST. 4. Open something page with very long title, for example: https://github.com/mozilla/mozregression/pull/465 5. Put the mouse cursor onto the item for the page in the sidebar, and wait for a while. # Expected result The page title is shown as a tooltip, styled like as regular tooltip (ex. on toolbar buttons) # Actual result The page title is shown as a floating text, with no background color. (Please see the attached screenshot also.)

Sorry I missed an important condition. To reproduce the problem, I need to set "extensions.webextensions.remote" to "false". It is false by default on Linux, but true by default on Windows.

Mozregression's result says: # The last good build app_name: firefox build_date: 2018-07-09 14:02:55.353000 build_file: C:\Users\clearcode\.mozilla\mozregression\persist\140937d55bd0--mozilla-inbound--target.zip build_type: inbound build_url: https://queue.taskcluster.net/v1/task/eyRSVJsJT4WGMysouGUC_w/runs/0/artifacts/public%2Fbuild%2Ftarget.zip changeset: 140937d55bd0babaaaebabd11e171d2682a8ae01 pushlog_url: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=140937d55bd0babaaaebabd11e171d2682a8ae01&tochange=e711420b85f70b765c7c69c80a478250bc886229 repo_name: mozilla-inbound repo_url: https://hg.mozilla.org/integration/mozilla-inbound task_id: eyRSVJsJT4WGMysouGUC_w # The first bad build app_name: firefox build_date: 2018-07-09 build_file: C:\Users\clearcode\.mozilla\mozregression\persist\2018-07-09--mozilla-central--firefox-63.0a1.en-US.win64.zip build_type: nightly build_url: https://archive.mozilla.org/pub/firefox/nightly/2018/07/2018-07-09-22-12-47-mozilla-central/firefox-63.0a1.en-US.win64.zip changeset: 19edc7c22303a37b7b5fea326171288eba17d788 pushlog_url: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=ffb7b5015fc331bdc4c5e6ab52b9de669faa8864&tochange=19edc7c22303a37b7b5fea326171288eba17d788 repo_name: mozilla-central repo_url: https://hg.mozilla.org/mozilla-central

After more research, I've realized that this problem affects to more tooltips. * In the tab bar - "List all tabs" button * In the navigation toolbar - "Home" button - Elements in the location bar (security information, "Show History" button, "..." button, "Pocket" button and "Bookmark" button) - The hamburger button - "Sign in to Sync", "Tracking Protection", and more items under the hamburger menu - Toolbar buttons added by addons

https://hg.mozilla.org/integration/mozilla-inbound/rev/e711420b85f7 This change seems expecting that style rules loaded from toolkit/content/widgets.css to be applied to all XUL <tooltip>s. However, it is actually applied only for <tooltip>s defined in browser.xul, and <tooltip default="true"> element dynamically inserted by Gecko itself looks not applied.