Say a website on my localhost takes about 3 seconds to do each request. This is fine, and as expected (as it is doing some fancy networking behind the scenes).
However, if i open the same url in tabs (in firefox), then reload them all at the same time, it appears to load each page sequentially rather than all at the same time. What is this all about?
Have tried it on windows server 2008 iis and windows 7 iis
It really depends on the web browser you are using and how tab support in it has been programmed.
It is probably using a single thread to load each tab in turn, which would explain your observation.
Edit: As others have mentioned, it is also a very real possibility the the webserver running on your localhost is single threaded.
network.http.max-connections 60
network.http.max-connections-per-server 30
The above two values determine how many connections Firefox makes to a server. If threshold is breached, it will pipeline the requests.
Each browser implements it in its own way. The requests are made in such a way to maximize the performance. Moreover, it also depends on the server (localhost which is slower).
If I remember correctly HTTP standard limits the number of concurrent conections to the same host to 2. This is the reason highload websites use CDNs (content delivery networks).
Your local web server configuration might have only one thread, so every next request will wait for the previous to finish