Please note: this is not the right answer, although I hope it continues to be useful. NB it has been made a “Community” answer so I don’t receive any points from upvotes
To see all commits for a specific branch (so this does NOT actually answer the original question, which is to see commits across all branches):
Click “Code” (left-most tab) on the main page for the repository. Under those 4 buttons (“master”, “Go to file”, “Add file”, “Code”) there is a blue rectangle. At the right end of that is a clock icon and a number. If the viewport of your browser is wide enough it even includes (hurrah) the word “commits”. This is a link. Click and ENJOY!!!
NB the URL for this page is like this: https://github.com/myProfile/myRepo/commits/master
