Because it does. When it takes a full 40 seconds, if not even more, before I am able to select a bookmark or type an entry into a search engine field, then something is not working right. (It is especially galling when the Firefox "Health Report" nevertheless claims "startup" times in the mid-teens.) I distinctly remember that this started to be a problem after whatever update it was came out back in March 2017, and it has persisted ever since. I'm absolutely sick of it. (I'm also sick of not being able to see just how big of a download each update will be; would it really be that hard to include it in the info page?) And no, I haven't added any hardware, changed any drivers, or done any of the usual bolshoi sidestepping questions that are typically asked in this case. Bottom line, Mozilla changed something in March '17, and FF hasn't been the same ever since.