Before you used to be able to have multiple pages and switch between tabs and the download timer before actually downloading would still continue counting down. I don't understand if this is a bug or intentionally put in for "bandwidth" but as someone who sometimes downloads multiple addons at a time and goes back to the addon page to read information while downloading it'd be great to have the download go instead of wasting extra time just for the timer to finish and then download. Especially for people with slower internet speeds I can see how this can get annoying if they just want to finish their downloads.
I wouldn't mind as much if it were 5 seconds though it probably will never go back to being that short to manage server bandwidth which I can understand, but the 15-20 second waiting time ontop of not being able to switch back tabs does seem like overkill with the amount of addons to get on here.
It seems they reverted it back to allowing parallel downloads, I honestly don't mind the 15-20 wait times for downloads since it helps with bandwidth costs or they want to display ads for that amount of time. Although I'm personally not able to donate to this site even if its one time fee I'd much rather have some ads on the download and addon page while disabling my adblocker to help keep this site free. Thanks for bringing attention to this!