Do you want to preview your project without publishing it? To do so click on the Preview icon and a player will be loaded over your project. This player shows you the most accurate and reliable view of the contents and interactivities of your project. The only difference is the video quality because the high quality clips of the projects are generated after the first publishing the project. If you observe any difference between published and preview mode versions of your project, after saving and publishing it, you need to empty the navigation history of your browser.
The yellow progress bar is only visible on Preview mode to help navigating the project. If you want your project to feature a progress bar once published, remember you need to add the Progress Bar addon to the timeline during the process of creating your composition.
By clicking the Preview button, the player opens up the project in the mobile view of it. It is really important previewing your project that way during the edition process because the user experience in mobile phone is different and must be taken into account. After switching the type of preview in the controls of Timeline, this setting of workflow will be saved unless changed.
In the screenshot above you can see how a Preview is selected by clicking either a desktop or a cell phone icon. The progress bar of the preview mode also displays the type of device when vídeo is played. The screenshot below, shows how to activate and play a desktop preview mode.