Tried using this script for Safari and Reddit. It works great with Chrome and Gmail.
Got the Reddit part working with Chrome just can't figure it out with Safari.
set _win to false
tell application "Safari"
set {idList, urlList} to {id, URL} of every tab of every window
end tell
set AppleScript's text item delimiters to return
if (urlList as text) contains "https://www.reddit.com" = true then
set theWin to 1
repeat with i in urlList
set theTab to 1
repeat with n in i
if n starts with "https://www.reddit.com" then
set {_win, _tab} to {theWin, theTab}
end if
set theTab to theTab + 1
end repeat
set theWin to theWin + 1
end repeat
end if
if _win ≠ false then
tell application "System Events"
if quit delay ≠ 0 then set quit delay to 0
tell process "Safari"
perform action "AXRaise" of window _win
end tell
end tell
tell application "Safari"
tell front window to set active tab index to _tab
end tell
else
tell application "Safari"
set newWin to make new window
tell newWin to set URL of active tab to "https://www.reddit.com"
end tell
end if