Usually when I have this issue in Chrome I just Bookmark -> Bookmark All Tabs -> Create a New Folder "Project A" do the same for "Project B". When I need to get back I open all the tabs in the Project x folder.
If you are on a Mac you can go a step further and create different desktops for different projects, the only draw back is if you accidentally Cmd + Q an app that is open on multiple desktops.