Sometimes, the Go Back/Forward menu commands and toolbar items remain disabled although there is a history of previous/next pages.
This forum is an example. In a new window, go to https://discourse.omnigroup.com/c/other-omni-apps/omniweb, then click on some topic. Although the window content changes to one specific discussion, you cannot go back to the table of contents via the Go Back command.
This is not a problem in this case, as you can always click on the OmniWeb entry on the top of the web page and will be back to the table of contents page. But on other websites, this alternative might be missing, leaving no way to go back.