Bugzilla

I still cannot reproduce this behavior. No address bar focus action can be observed when pressing the "CTRL" + "TAB" keys while a single tab is opened in the browser. This is been checked in Nightly v71.0a1 from 2019-09-15, Beta v70.0b6 and Release v69.0.

This being said, I cannot regress the issue / attempt to find the regressor. Elliot, I have to ask you to help us determine the regressor. 

Please use these steps: 
1. You have to determine a build that does not reproduce the issue.
Considering that the 3 main version of the browser, firefox69, firefox68, firefox67 reproduces this issue (for you), then you should probably look back to older versions and try to find one that does NOT reproduce it:
   a. Open mozregression-gui.exe (https://github.com/mozilla/mozregression/releases/download/gui-0.9.39/mozregression-gui.exe)
   b. Click "File" -> "Run a single build"
   c. On "Basic configuration" screen, select Build Type: "opt" and click "Next" button. 
   d. Skip "Profile selection" screen by the "Next" button.
   e. In the "Single run wizard" screen, "Build from:" section, select "release" instead of "date" and then select a release number under 67.
   f. The mozregression app will open the selected build. Try to reproduce the issue and remember the release chosen.
   g. Repeat steps b. to e. until you find a build that does not reproduce the issue; Remember it.
   h. If even builds older than release 20 reproduce the issue, than you can consider this issue as not a regression and stop the investigation.
2. You will use mozregression app to "bisect" builds that reproduce the issue by builds that do not reproduce it in search of the one build/changeset that introduced the issue, in the first place: 
   a. Open mozregression-gui.exe
   b. Click "File" -> "Run a new bisection"
   c. On "Basic configuration" screen, select Build Type: "opt" and click "Next" button. 
   d. Skip "Profile selection" screen by the "Next" button.
   e. On the Bisection wizard screen, you will need to select a build that reproduces the issue and one that does not:
     e1. In the "Last known good build:" section, select "release" on the right drop-down and the release number that you found that does NOT reproduce the issue.
     e2. In the "First known bad build:" section, select "release" on the right drop-down and a release number that you know to reproduce the issue, which are any other builds that you tested before and found to reproduce it (the earlier the build chosen, the faster it will be to run the bisection).
   f. Click "Finish" to start the bisection process.
   g. Builds will open one-by-one, you will need to test each one of them and see whether the issue reproduces. If it reproduces, then you need to select the "bad" button in the mozregression window and if not, you need to select the "good" button.
   h. When bisection is done, you will have the information in the "Log View" section of the mozregression window; bisection may also fail due to not enough builds, but the logs can always be useful. 
3. Copy the logs in a text file and attach it to this bug.

If there is still information you need regarding the regression process, please request information from me.

Thank you for your contribution!

I finally understood what the issue is here: the reporter sais that in firefox69, firefox70 and firefox71, when only one tab is opened, if he presses the "CTRL" + "TAB" keys together, then the focus would move from the content section to the address bar and back.
He suggests that this behavior should be removed (as firefox68 works now, no action on pressing that key combo.)
I have confirmed this behavior on Windows 10 and Mac OS 10.13.6.