User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:55.0) Gecko/20100101 Firefox/55.0 Build ID: 20170422030205 Steps to reproduce: Enable Custom Tabs and click on links in 3rd party Twitter apps to open them in Custom Tabs. Use Custom Tabs for a while to open dozens of others links. Close them, open more links, close, repeat multiple times. Doesn't happen immediately. From a 3rd party Twitter client (because the official one doesn't open Custom Tabs for some reason) open link from this tweet https://twitter.com/PamelaParesky/status/855809217076371456 Actual results: Custom Tabs loads the page with a red bar below the address bar. It's about as thick as the address bar and loads simultaneously with the address bar, so it's not part of the website. Once the red bar appears, it's more likely to appear on other pages too. Does not happen with every link, but it's 100% reproducible with a link that gets the bar. It can happen while opening links from Gmail too, not just Twitter. How to remove the red bar: 1. Disable Custom Tabs. 2. Close Nightly and swipe it to remove from Android Recents. 3. Start Nightly and enable Custom Tabs. 4. Repeat Step 2 (doesn't work without this) 5. Open a previously affected link again. No red bar... at least for a while. Expected results: It should load a page without a red bar. See the screenshots.

Red bar below the address bar in Custom Tabs.

Everything was working fine. I tried to reproduce the red bar by opening and closing the same Washington Post link from the screenshot, total of 6 times. I would open the link, press back to go back to Flamingo (Twitter client), then repeat 6 times. Then I opened Nightly to see what's in the tab manager. There were 6 identical WaPo links there, meaning whatever Custom Tab opens, it keeps them in Nightly's tab manager and doesn't remove when I press the back button to close Custom Tab and go back to Flamingo. When I finished looking the Night tab manager, I pressed Home then opened Flamingo and opened the same WaPo link with Custom Tabs the 7th time. This time Nightly crashed. Here is the report: bp-95efcb4e-65e6-4fac-8726-a8f6f0170422 and after I pressed to restart Nightly from the crash screen, the red bar bug returned. The browser doesn't necessarily have to crash in order for the red bar to return, but any crash I've seen so far brings back the red bar, with 100% consistency. Here is another crash that I just had that brought the red bar. It was caused by the landscape mode crashing Custom Tabs: bp-e7e2039a-0469-4c62-8d12-248390170422 Should I file a separate bug for this? I can't seem to reproduce it. One interesting thing I noticed is when I hold the phone in portrait mode and open an affected link, the red bar loads simultaneously with the address bar, before the website loads. If I then shift the phone to landscape mode (after the site is loaded), the red bar appears to be part of the website UI loads synchronous with the rest of the website UI, after the address bar is loaded. If I shift from landscape back to portrait, it again appears to be part of the website because it loads after the address bar, synchronized with Washington Post's black menu bar on top. As I was typing this, I disabled re-enabled Custom Tabs and next time when I tried to open a link with it, it crashed. The red bar returned afterwards: bp-62069524-06e4-464c-9cea-afbbe0170422

If this started happening only very recently, it's probably bug 1358805.

(In reply to Jan Henning [:JanH] from comment #3) > If this started happening only very recently, it's probably bug 1358805. It's been happening since yesterday. That's when I started using Nightly for the first time.