STR: 1. Visit https://addons.mozilla.org/en-US/firefox/addon/furfox-tail-twister/ and click "Add to Firefox" 2. Look at the Firefox Hello (aka Loop) chat-bubble icon in your toolbar. EXPECTED RESULTS: Nice solid black outline around the chat-bubble icon. ACTUAL RESULTS: Its top, left, and right edges are clipped. (Not sure if it's mis-positioned, mis-sized, or what.) This regressed recently -- first bad Nightly is 2016-02-05. Tighter regression range from mozregression: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=f53533d9eb771f3251921949ab2c888def70f41f&tochange=5e024441510f6d2b460e570d0e6d2dee0dc89723 That range includes some Loop-specific changes (bug 1154277) -- that seems most likely to have caused this, at first glance. I'm using a 64-bit linux nightly, with a fresh profile (aside from adding a lightweight theme in the STR).

Here's a screenshot from before this regressed, for comparison.

Sorry, my initial guess at the regressing bug was wrong. From bisecting on fx-team (with mozregression), I got this (tighter) regression range: https://hg.mozilla.org/integration/fx-team/pushloghtml?fromchange=16a675e05315e798fcd5990f983bac910b685d71&tochange=d577f0c34dee0bf5d0054bea3d8535af03f2b85d This seems to be just: > Mark Banner — Bug 1239828 - Update Loop to the latest version. r=Standard8 for import of already reviewed code. ...which means this probably regressed during the Loop development life cycle (between last version & the "latest version" imported here).

We're tracking it. Exact cause is in bug 1246316