Sideways is great but not good enough to avoid scrolling. There WAS a trick. (Stamping my feet.) Whoever knows how is sleeping. Maybe tomorrow s/he will give us the secret. Will ping you.
Go to the forum you want to be in where you see the double column layout... double click on the comments section and the screen will zoom into just the single column of the comment. Scroll down and up only in that section. Done.
Clicking on a link will take you to a new tab window and retain that size and orientation. You can return to your previous tab window by clicking the tab window selector at the lower right and selecting the window you want.
I hope this helps.