with all do respect !! for me Palemoon still remain in top list as a secondary daily browser but i'm still in research and still testing because unfortunately its not working everywhere as supposed !! so speaking about issue, im not a developer but i have enough knowledge to understand that something is related to the browser itself who creating this issues when trying to bid in ebay !! and don't get me wrong im not defending ebay i think they are lazy *** who don't want to optimize that heavy webpage but lets be honest i have few images i did at the same time in different browsers im testing and here the result !!
Palemoon 32.01 Fail
SeaMonkey 2.53.15 Fail
Ice Dragon 188.8.131.52 (32-bit) working well
K-melon 76.4.7 I couldn't log in on ebay
Waterfox G184.108.40.206 (64-bit) working well
All these browsers are portable working from USB > this is what I need ! couldn't find the best one yet, all of them have some issues ! so i cannot point as you said to where is the issue but certainly is something related to the browser if different browsers at the same scenario behave different ! I hope you'll find a solution for that and this is only one of the problem which other don't have ... I shortly put below general examples how they working in different conditions !!
Palemoon = light, acceptable speed most of the time, not slow in general apart from YouTube its just horrible slow most of the time freezing, needs time to recover, compatible in general apart from ebay issues, nice simple interface.
SeaMonkey = not heavy but not the lightest, one of the fastest for browsing, the fastest in YouTube (apart from k-melon which using mobile YouTube), same ebay issues, complicated UI and not that easy to use !
Ice Dragon = heavy like new firefox, not that fast on browsing, slow in youtube little better than Palemoon, high compatibility
K-melon = the lightest and the fastest browser but not easy and not the most intuitive UI and some serious incompatibilities,including ebay and other pages, youtube is mobile version but fast.
Waterfox = very similar with ice-dragon, trying to find a difference between these 2 !!