Do you think your internet speed is fast like viewing webpages, etc?
A quick
google search reveals a possible Firefox bug but I have my doubts as you have only in last 10 days had the problem.
Have you installed any software or changed any settings in last two weeks maybe?
Also, could you click on 'Run' from the start menu and type in "CMD"
Now within the 'command box window', can you type "ipconfig /flushdns" and press <enter?
Now click on the 'X' or type "exit" to close the box and clear the cache of your browser.