Using Firefox under (sigh) Windows, I find that Home & End do not work unless control-shifted. Initially, Page Up & Page Down do not work at all, but they both work once you have done a control-shifted Home or End.

In the main Forum window, if I click on the left margin *and then hit the down arrow key*, the corresponding page will be highlighted so that I can call it up with the Enter key rather than have to use the mouse. I can continue to use down arrow & Enter for subsequent lines, so long as I do not post on a page. If I do that & go back to the main window (using Back Space), I have to go thru the down-arrow ritual again.